This case concerns the validity of 45 CFR § 233.100(a)(1) (1976),1 a regulation promulgated by the Secretary of Health, Education, and Welfare (HEW) pursuant to a delegation of rulemaking authority in § 407(a) of the Social Security Act, 42 U.S.C. § 607(a).2 The issue is whether the regulation is a proper exercise of the Secretary's statutory authority.

* The statute is contained in the Social Security Act's Title IV, which has to do primarily with Aid to Families with Dependent Children (AFDC). The AFDC program was established by the Act in 1935 to provide welfare payments where children are needy because of the death, absence, or incapacity of a parent. 42 U.S.C. § 606(a). The original conception of AFDC was to allow widows and divorced mothers to care for their children at home without having to go to work, thus eliminating the practice of removing needy children in situations of that kind to institutions. See Burns v. Alcala, 420 U.S. 575, 581-582, 95 S.Ct. 1180, 1184-1185, 43 L.Ed.2d 469 (1975). AFDC was not originally designed to assist children who are needy simply because the family breadwinner is unable to find work; it was contemplated that other programs would alleviate that problem by attacking unemployment directly. See Carleson v. Remillard, 406 U.S. 598, 603, 92 S.Ct. 1932, 1935, 32 L.Ed.2d 352 (1972); King v. Smith, 392 U.S. 309, 313, 327-329, 88 S.Ct. 2128, 2131, 2138-2139, 20 L.Ed.2d 1118 (1968). Other parts of the Act encouraged the establishment of state unemployment compensation programs, primarily through tax incentives, but the federal role in these programs is not so great as in AFDC. See Ohio Bureau of Employment Services v. Hodory, 431 U.S. 471, 97 S.Ct. 1898, 52 L.Ed.2d 513 (1977).

Title IV was amended in 1961 to add § 407. Pub.L. 87-31, § 1, 75 Stat. 75. This section established an experimental program (AFDC-UF)3 to provide assistance in some cases where the unemployment of a parent causes dependent children to be needy. The States were given broad power to define "unemployment" for purposes of the program and to determine the relationship of this new program to existing state unemployment compensation plans. In 1968 the AFDC-UF program was made permanent, 81 Stat. 882, but the eligibility criteria were modified to withdraw some of the definitional authority delegated to the States. The statute now requires a participating State to provide assistance where a needy child "has been deprived of parental support or care by reason of the unemployment (as determined in accordance with standards prescribed by the Secretary) of his father." 42 U.S.C. § 607(a). See Philbrook v. Glodgett, 421 U.S. 707, 709-711, 95 S.Ct. 1893, 1896-1897, 44 L.Ed.2d 525 (1975).4

Both AFDC and AFDC-UF are cooperative ventures of the Federal Government and the States. States that elect to participate in these programs administer them under federal standards and HEW supervision. Funding is provided from state and federal revenues on a matching basis. See, e. g., Shea v. Vialpando, 416 U.S. 251, 253, 94 S.Ct. 1746, 1750, 40 L.Ed.2d 120 (1974); King v. Smith, 392 U.S., at 316, 88 S.Ct., at 2132. Although every State currently participates in AFDC, only about half the States participate in the AFDC-UF program. Dept. of HEW, Public Assistance Statistics, Oct. 1976, table 5, p. 9 (1977).

The instant case originated in 1971 as a challenge to Rule 200.X.(A)(2) of the Maryland Department of Employment and Social Services. That Rule denies AFDC-UF benefits to families where the father is out of work for reasons that disqualify him for state unemployment insurance compensation.5 The original plaintiffs represented two classes of families with dependent children who were thereby ineligible for AFDC-UF benefits: one where the father had been discharged for misconduct (excessive absenteeism), and the other where the father was out of work because of a strike. The defendants were Maryland officials having responsibility for the administration of public assistance grants in the State. A three-judge United States District Court was convened to consider the claim that Rule 200.X.(A)(2) violated the Equal Protection Clause of the Fourteenth Amendment. The court sustained the constitutionality of the state regulation but went on to hold it invalid because it was contrary to the federal regulation prescribing standards for the determination of unemployment under the AFDC-UF program. Francis v. Davidson, 340 F.Supp. 351 (Md.), summarily aff'd, 409 U.S. 904, 93 S.Ct. 223, 34 L.Ed.2d 168 (1972) (Francis I ). Although HEW did not agree that its regulation was inconsistent with Rule 200.X.(A)(2), the Solicitor General, in his memorandum for the United States as amicus curiae, filed in Francis I at this Court's invitation, 408 U.S. 920, 92 S.Ct. 2495, 33 L.Ed.2d 330 (1972), suggested a summary affirmance in that case in light of the then-forthcoming revision of the HEW regulation.

The HEW regulation, as amended, expressly, authorizes some state discretion in defining unemployment. Generally, it requires the States to consider a person to be unemployed for AFDC-UF purposes if he works less than 100 hours a month, except for intermittent employment, and "except that, at the option of the State, such definition need not include a father whose unemployment results from participation in a labor dispute or who is unemployed by reason of conduct or circumstances which result or would result in disqualification for unemployment compensation under the State's unemployment compensation law." 45 CFR § 233.100(a)(1) (1976). The Secretary had stated that the purpose of this amendment was to nullify the effect of Francis I by making explicit the HEW policy of allowing the States to exclude AFDC-UF participants based on the particular reason that the father was out of work.6

After the amended HEW regulation became effective, the defendant Maryland officials moved that the District Court dissolve its earlier injunction issued March 16, 1972, after Francis I had been decided, against enforcement of Rule 200.X.(A)(2). That court recognized that "(t)he conflict between the federal and the Maryland regulation ended after the former was amended," but nevertheless it denied the motion and continued the injunction on the ground that the amended federal regulation now was in conflict with the federal statute. Francis v. Davidson, 379 F.Supp. 78, 81 (Md.1974) (Francis II ). First, with regard to the class of fathers discharged for misconduct, the District Court stated that these people are necessarily "unemployed," within the meaning of the statute, and that any contrary regulation is invalid. Second, the court recognized that it is not clear whether the statutory term "unemployed" includes persons involved in a labor dispute. The court held, however, that the HEW regulation was invalid in this regard because it delegated the question of coverage to the States without providing a uniform national standard. Id., at 81-82.

After this Court dismissed a direct appeal in Francis II for want of jurisdiction, 419 U.S. 1042, 95 S.Ct. 614, 42 L.Ed.2d 636 (1974), appeals were taken by the state defendants and by the Chamber of Commerce of the United States, as intervenor, to the United States Court of Appeals for the Fourth Circuit. There the case was consolidated with an appeal in a similar case. Bethea v. Mason, 384 F.Supp. 1274 (Md.1974), where a single District Judge had followed Francis II in holding the same HEW regulation invalid insofar as it authorized the State to deny AFDC-UF benefits to fathers who had voluntarily quit their previous jobs.

The Fourth Circuit affirmed the three appeals in an unpublished per curiam adopting the respective opinions of the two District Judges. See 529 F.2d 514 and 515 (1975). The state defendants petitioned for certiorari, contending that the current HEW regulation is authorized by the federal statute and that the injunction against the state regulation therefore should be dissolved.7 The Solicitor General, at the invitation of the Court, 425 U.S. 969, 96 S.Ct. 2164, 48 L.Ed.2d 792 (1976), filed a memorandum for the United States as amicus curiae, supporting the state defendants' position. We granted certiorari. 429 U.S. 939, 97 S.Ct. 352, 50 L.Ed.2d 307 (1976).

The ultimate question in this case is whether the statutory term "unemployment" may be interpreted to allow the State to exclude the three classes of respondents from receiving AFDC-UF benefits. There can be no doubt that 45 CRF § 233.100(a)(1) (1976) embodies that interpretation. Thus, the actual issue we must decide is not how the statutory term should be interpreted, but whether the Secretary's regulation is proper.

(1-3) Ordinarily, administrative interpretations of statutory terms are given important but not controlling significance. This was the Court's approach, for example, when it had under consideration the question whether the term "wages" in Title II of the Social Security Act included a backpay award. Social Security Board v. Nierotko, 327 U.S. 358, 369, 66 S.Ct. 637, 643, 90 L.Ed. 718 (1946).8

Unlike the statutory term in Title II, however, Congress in § 407(a) expressly delegated to the Secretary the power to prescribe standards for determining what constitutes "unemployment" for purposes of AFDC-UF eligibility. In a situation of this kind, Congress entrusts to the Secretary, rather than to the courts, the primary responsibility for interpreting the statutory term. In exercising that responsibility, the Secretary adopts regulations with legislative effect. A reviewing court is not free to set aside those regulations simply because it would have interpreted the statute in a different manner. American Telephone & Telegraph Co. v. United States, 299 U.S. 232, 235-237, 57 S.Ct. 170, 172, 81 L.Ed. 142 (1936).9

The regulation at issue in this case is therefore entitled to more than mere deference or weight. It can be set aside only if the Secretary exceeded his statutory authority or if the regulation is "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." 5 U.S.C. §§ 706(2) (A), (C).10

(4) We turn now to the grounds on which the District Courts and the Court of Appeals held the regulation invalid, keeping in mind the narrow scope of review that is indicated in this situation.

These courts held that the Secretary exceeded his statutory authority to prescribe standards, in the first place, because he permitted the determination of eligibility to turn in part on the reason for the father's unemployment. The language of § 407(a) was thought to make the only relevant consideration that of whether, not why, the father was out of work:

" 'A man out of work because he was discharged for cause by his employer is unemployed. There can be no two ways about that conclusion'. . . . (N)o combination of federal and state regulations may provide that a father who is unemployed is not unemployed." Francis II, 379 F.Supp., at 81, quoting Francis I, 340 F.Supp., at 366.

And in Bethea the court by like reasoning held that a person who voluntarily quit his job is to be considered unemployed within the meaning of the statute. 384 F.Supp., at 1280-1281.

We do not agree that the statutory language is so unambiguous. The term "unemployment" is often used in a specialized context where its meaning is other than simply not having a job. For example, the concept of unemployment is frequently limited to persons who have some connection with the work force, that is, individuals who desire to work and are capable of working, and who, usually but not always, have held jobs in the past. In addition, the feature of involuntariness is often linked with unemployment. Limitations of this nature are found in the definitions used by the Department of Labor in compiling unemployment statistics.11 State unemployment compensation programs generally confine their benefits in this manner.12 Indeed, the other provisions of s 407 impose similar limitations, indicating that the AFDC-UF program was not intended to provide assistance without regard to the reason a person is out of work.13

Thus, we conclude that the statutory term is capable of more than the tautological definition imposed by the District Judges and the Court of Appeals. Congress itself must have appreciated that the meaning of the statutory term was not self-evident, or it would not have given the Secretary the power to prescribe standards.

Respondents argue, however, that Congress intended that the Secretary prescribe an "hours-worked" standard for determining unemployment but did not intend any further additions to the eligibility criteria specified in other provisions of the statute. In fact, a minimum hours-worked standard is part of the regulation at issue in this case, but there is no indication in the statutory language or legislative history that Congress intended to foreclose other factors in the determination of what constitutes unemployment for purposes of the AFDC-UF program.

Of course, the Secretary's statutory authority to prescribe standards is not unlimited. He could not, for example, adopt a regulation that bears no relationship to any recognized concept of unemployment or that would defeat the purpose of the AFDC-UF program. But the regulation here at issue does not even approach these limits of the delegated authority. By allowing the States to exclude persons who would be disqualified under the State's unemployment compensation law, the Secretary has incorporated a well-known and widely applied standard for "unemployment." Exclusion of individuals who are out of work as a result of their own conduct and thus disqualified from state unemployment compensation is consistent with the goal of AFDC-UF, namely, to aid the families of the involuntarily unemployed.14 On the other hand, state unemployment benefits are ordinarily available only after a waiting period and only for a limited number of weeks or months. By providing benefits during the periods before and after state unemployment compensation is available, AFDC-UF fills a significant gap in social insurance coverage.15 Thus we cannot say that the Secretary's regulation defeats the purpose of the AFDC-UF program.

We therefore hold that the HEW regulation, to the extent it allows the States to determine that persons disqualified under unemployment compensation laws are not "unemployed" under § 407(a), is within the statutory authority delegated to the Secretary, and is reasonable.

(5, 6) The second stated reason for the District Judges' and Court of Appeals' holding that the Secretary's regulation was invalid was that it permitted the States the option of denying unemployment compensation benefits to participants in a labor dispute.16 Although the holding is not entirely clear to us, it appears that what was regarded as fatal was the Secretary's failure to impose sufficient standards to control the States' decisions under this optional feature.17 Presumably, the same rationale would provide an alternative basis for holding the regulation invalid to the extent it allows States the uncontrolled option of denying benefits to persons who were discharged for cause or had voluntarily quit their jobs.

It is clear that a major purpose of the 1968 amendment was to retract some of the authority previously delegated to the States under § 407(a). Philbrook v. Glodgett, 421 U.S., at 710, 95 S.Ct., at 1896. We, however, do not think this shift of authority from the States to the Secretary required the Secretary to adopt a regulation that precludes any recognition of local policies. If Congress had intended such a result, it might have changed the statutory language from "unemployment (as defined by the State)" to "unemployment (as defined by the Secretary)." Instead, § 407(a) now reads "unemployment (as determined in accordance with standards prescribed by the Secretary)." The power to "determine" unemployment remains with the States, and we conclude that the power to prescribe "standards" gives the Secretary sufficient flexibility to recognize some local options in determining AFDC-UF eligibility.

The legislative history, we acknowledge, is at some variance with the statutory language. The effect of the 1968 amendment is described as to "provide for a uniform definition of unemployment throughout the United States," and as to "authorize a Federal definition of unemployment by the Secretary." S.Rep. No. 744, 90th Cong., 1st Sess., 3-4, 160; U.S.Code Cong. & Admin.News 1967, pp. 2834, 2997 (1967). See H.R.Rep. No. 544, 90th Cong., 1st Sess., 3, 17, 108 (1967); 113 Cong.Rec. 32592 (1967) (remarks of Sen. Long). We do not understand these comments to mean, however, that the Secretary is prohibited from allowing the States any options in determining whether or not a person is "unemployed" for purposes of the AFDC-UF program. First, the legislative history cannot be read literally in its claim that the amended statute itself provides a federal definition of unemployment; at best the statute delegates to the Secretary the power to prescribe such a definition. Second, we have no quarrel with the statements in the legislative history that the Secretary is authorized to adopt such a uniform definition; we simply hold that he is not required to do so.

Certainly, the congressional purpose was to promote greater uniformity in the applicability of the AFDC-UF program. But the goal of greater uniformity can be met without imposing identical standards on each State. In one case, for example, a State was permitted to adopt a somewhat more liberal hours-worked test than the minimum required by the Secretary. Macias v. Finch, 324 F.Supp. 1252 (ND Cal.), summarily aff'd, 400 U.S. 913, 91 S.Ct. 180, 27 L.Ed.2d 153 (1970). We conclude, therefore, that the Secretary's approach in the present case is not contrary to the purpose of the statute.

Our conclusion is reinforced by our understanding of the AFDC-UF program as involving the concept of cooperative federalism. The States are free not to participate in the program, and, as we have noted, only about half of them in fact do so. The congressional purpose is not served at all in those States where AFDC-UF is totally unavailable. Accordingly, we should not lightly infer a congressional intention to preclude the Secretary from recognizing legitimate local policies in determining eligibility. See New York Dept. of Soc. Services v. Dublino, 413 U.S. 405, 413-414, 421-422, 93 S.Ct. 2507, 2512-2513, 2516-2517, 37 L.Ed.2d 688 (1973).

We therefore hold that 45 CFR § 233.100(a)(1) (1976) adequately promotes the statutory goal of reducing interstate variations in the AFDC-UF program. In this respect, the regulation is both reasonable and within the authority delegated to the Secretary.

The judgment of the Court of Appeals is reversed.

It is so ordered.

Mr. Justice WHITE, with whom Mr. Justice BRENNAN, Mr. Justice MARSHALL, and Mr. Justice STEVENS, join, dissenting.

The regulation under review in this case, 45 C.F.R. § 233.100(a)(1) (1976), provides that for purposes of the AFDC-UF program, the definition of unemployment need not include, "at the option of the State," a father whose unemployment results from a labor dispute or some conduct that would disqualify him under the State's unemployment compensation law. (Emphasis added.) The Court today sustains this regulation notwithstanding its recognition that "a major purpose of the 1968 amendment was to retract some of the authority previously delegated to the States under § 407(a)." Ante, at 430. The Court reasons, without citation to legislative authority, that "the goal of greater uniformity can be met without imposing identical standards on each State." Ante, at 431. Contrary to the majority, I do not believe that the legislative history reflects a congressional intent to achieve merely "greater uniformity" in the definition of unemployment; the legislative record plainly reveals that Congress contemplated a federal definition of unemployment applicable to all States that adopt the AFDC-UF program. Since I do not believe that the subject regulation conforms to this congressional mandate, I would affirm the judgment of the Court of Appeals.

The Court acknowledges that the legislative history is "at some variance" with its position. Ante, at 430. This understates the case; literally all of the relevant legislative history repeatedly and unequivocally affirms the strong congressional objective of creating a federal definition of unemployment. It is common ground that Congress changed the wording of § 407(a) from "unemployment (as defined by the State)" to "unemployment (as determined in accordance with standards prescribed by the Secretary)" for the express purpose of "eliminat(ing) the variations in state definitions of unemployment." Philbrook v. Glodgett, 421 U.S. 707, 719, 95 S.Ct. 1893, 1901, 44 L.Ed.2d 525 (1975). But the Court would have us believe that the statute nevertheless contemplates a regulation leaving it completely within state discretion whether to cover those not working by reason of labor disputes or because of discharge for cause.* In my view, this is flatly contrary to the thrust of the legislative history, which bears some recitation.

In the Senate, most of the work on the 1968 amendments was done by the Finance Committee. That Committee reported that the bill would

"(e) modify the optional unemployed fathers program to provide for a uniform definition of unemployment throughout the United States." S.Rep. No. 744, 90th Cong., 1st Sess., 4 (1967); U.S.Code Cong. & Admin.News 1967, pp. 2834, 2837 (emphasis added).

"A major characteristic of the existing law is the authority left to the States to define 'unemployment.' The committee believes that this has worked to the detriment of the program because of the wide variation in the definitions used by the States. In some instances, the definitions have been very narrow so that only a few people have been helped. In other States, the definitions have been relatively broad. The committee bill is designed to correct this situation and to make other improvements in the program.

"The amendments proposed by the committee would authorize a Federal definition of unemployment by the Secretary . . . ." Id., at 160 U.S.Code Cong. & Admin.News 1967, p. 2996. (emphasis added).

The Ways and Means Committee, which carried the legislation in the House, adopted the same view:

"Under present law . . . (t)he definition of unemployment is left up to the individual States. Under the bill . . . the definition of unemployment would be made by the Federal Government." H.R.Rep. No. 544, 90th Cong., 1st Sess., 17 (1967) (emphasis added).

See also id., at 3, 108 (using language almost identical to that adopted by the Senate Finance Committee, S.Rep. No. 744, supra, at 3-4, 160).

The Undersecretary of HEW, Wilbur J. Cohen, expressed his Department's view that the new legislation would require a uniform national standard:

"Today, 22 States have programs to assist (children who are needy because their fathers are unemployed). But the differences between State programs are great. States may define unemployment as narrowly or broadly as they wish, requiring substantial previous work experience or no work experience. This variation in definition of unemployment is shown clearly by three adjacent Southwestern States, Arizona, Utah, and Colorado. Each of these States has a population of between 1 and 2 million, yet in Arizona only 19 families of unemployed parents received AFDC in May, while during the same month there were 880 in Utah and 1,600 in Colorado. Arizona's narrow definition of unemployment has kept its program to a token level.

"The House bill continues to allow States to choose whether they will include dependent children of unemployed parents under AFDC. But for the first time the House will set a Federal definition of unemployment. We are in complete agreement that there should be a Federal definition of unemployment established by the Congress and the Secretary." Hearings on H.R. 12080 before the Senate Committee on Finance, 90th Cong., 1st Sess., 268 (1967) (emphasis added).

The members of the Senate Finance Committee expressed no doubt as to the meaning of the Undersecretary's remarks: "Senator Williams: I notice you say you are in complete agreement that there should be a Federal definition of unemployment." Id., at 269 (emphasis added).

Finally, after the enactment of the 1968 amendments, the Senate Finance Committee was unequivocal in summing up the amendments to the unemployed fathers provisions: "The amendments provide for a Federal definition of unemployment for States which have AFDC-UF programs." Senate Committee on Finance, 90th Cong., 2d Sess., Report on Social Security Amendments of 1967 Pub.L. 248, Brief Summary of Major Provisions and Detailed Comparison with Prior Law 3 (July 15, 1968) (emphasis added). See also id., at 63 ("Unemployment will be defined by the Secretary of Health, Education, and Welfare"); 113 Cong.Rec. 23054 (1967) (remarks of Rep. Mills) ("(W)e found . . . that the fact that the definition of unemployment is left to the States has had unfortunate results. . . . The Bill would correct this situation"); id., at 32592 (remarks of Sen. Long) ("(T)here would be a Federal definition of 'unemployment' "); id., at 36373-36374 ("(T)he Secretary will prescribe standards for the determination of what constitutes unemployment. The term is defined by the States under present law"); Senate Committee on Finance and House Committee on Ways and Means, 90th Cong., 1st Sess., Report on Summary of Social Security Amendments of 1967, p. 17 (Comm. Print 1967) ("(T)he Secretary will prescribe standards for the determination of what constitutes unemployment").

Unlike the majority, I have no doubt that the legislative history means what it says and confines the regulatory authority of the Secretary; by amending § 407(a) to place the responsibility for defining unemployment on the Secretary, Congress intended to establish "a uniform definition of unemployment throughout the United States." S.Rep.No.744, supra, at 4; U.S.Code Cong. & Admin.News 1967, p. 2837; H.R.Rep.No.544, supra, at 3. While I agree with the majority that this Court should defer to any reasonable definition given by the Secretary to the term "unemployment," I cannot agree, in light of the legislative history, that the Secretary may simply delegate the responsibility for defining that term to the States, for in important respects this would simply return the law to the situation existing prior to the amendment defining that term to the States. Here, the Secretary has promulgated a regulation describing a rather broad category of individuals who may be eligible for AFDC-UF benefits but has then permitted the States to include or exclude those individuals from eligibility "at the option of the State." Contrary to the obvious intent of Congress, this leaves to state discretion the coverage of important categories of claimants and invites the very diversity in coverage that the 1968 amendment was designed to prevent. I cannot believe that this regulation conforms to the statutory purpose. Accordingly, I respectfully dissent.