MR. JUSTICE MARSHALL delivered the opinion of the Court. This appeal presents the question whether illegitimate children of a federal civil service employee are entitled to survivors' benefits under the Civil Service Retirement Act when the children once lived with the employee in a familial relationship, but were not living with the employee at the time of his death.

I

George Isaacson and the appellee Patricia Clark lived together from 1965 through 1971 without benefit of matrimony. They had two children, Shawn and Tricia Clark, born in 1968 and 1971, respectively, and the four lived together as a family. After the appellee and Isaacson separated, the appellee filed a state-court action in Montana seeking a determination of the paternity of the children. In June 1972, the Montana court issued a decree determining that Isaacson was the natural father of the children and ordering him to contribute to their support. Isaacson provided monthly support payments up to the time of his death in 1974.

At the time of death, Isaacson was a federal employee covered by the Civil Service Retirement Act, 5 U. S. C. § 8331 et seq. The Act provides that each surviving child of a deceased federal employee is entitled to a survivors' annuity. 5 U. S. C. § 8341 (e)(1). All legitimate and adopted children under 18 years of age qualify for these benefits, but stepchildren or "recognized natural" children under 18 may recover only if they "lived with the employee . . . in a regular parent-child relationship." 5 U. S. C. § 8341 (a)(3)(A). In September 1974, the Civil Service Commission's Bureau of Retirement, Insurance, and Occupational Health denied the appellee's application for such annuities for Shawn and Tricia. The Bureau held that 5 U. S. C. § 8341 (a) (3) (A) bars recovery for otherwise qualified children born out of wedlock who, like Shawn and Tricia, were not living with the employee

at the time of his death. The Commission's Board of Appeals and Review affirmed.1

The appellee then filed this action in the Court of Claims on behalf of her children. She argued that 5 U. S. C. § 8341 (a)(3)(A) allows recovery where, as here, the recognized natural children had once lived with the employee in a parent-child relationship. Alternatively she contended that, if the Commission's interpretation of 5 U. S. C. § 8341 (a) (3) (A) was correct, that provision violated the equal protection component of the Due Process Clause of the Fifth Amendment because it impermissibly discriminated against illegitimate children.

The Court of Claims granted the appellee's motion for summary judgment. 218 Ct. Cl. 705, 590 F. 2d 343. Ignoring the statutory issue, the court granted relief on the authority of its earlier decision in Gentry v. United States, 212 Ct. Cl. 1, 546 F. 2d 343 (1976), rehearing denied, 212 Ct. Cl. 27, 551 F. 2d 852 (1977), which held that the "lived with" requirement of 5 U. S. C. § 8341 (a)(3)(A) unconstitutionally discriminated against illegitimate children. We postponed consideration of our jurisdiction pending hearing on the merits, 441 U. S. 960 (1979), and now affirm on the statutory ground presented to but not addressed by the Court of Claims.2

1 On January 1, 1979, the Civil Service Commission was abolished, and the Office of Personnel Management assumed primary responsibility for the civil service retirement program. See Civil Service Reform Act of 1978, Pub. L. 95-454, 92 Stat. 1111; Reorg. Plan No. 2 of 1978, 3 CFR 323 (1979). For convenience, throughout this opinion we shall refer to the agency administering the retirement program as the Civil Service Commission.

2 The appellee contends that this Court does not have jurisdiction to entertain this appeal. We disagree.

By an order dated January 27, 1978, the Court of Claims held that the "lived with" requirement of 5 U. S. C. § 8341 (a) (3) (A) applicable to illegitimate children violated the equal protection component of the Due Process Clause of the Fifth Amendment. The court then resolved the issue

The Civil Service Retirement Act provides survivors' annuities to all legitimate children, but grants the same benefits to

of relief and entered final judgment on November 6, 1978. The Government filed its notice of appeal on December 5, 1978.

The appeal statute relied upon by the Government, 28 U. S. C. § 1252, provides:

"Any party may appeal to the Supreme Court from an interlocutory or final judgment, decree or order of any court of the United States . . . holding an Act of Congress unconstitutional in any civil action, suit, or proceeding to which the United States or any of its agencies, or any officer or employee thereof, as such officer or employee, is a party." (Emphasis added.)

The appellee first contends that the Government failed to file a timely notice of appeal because it did not appeal the January 27, 1978, decision on the liability issue. Section 1252 would have allowed the Government to seek review of this interlocutory order declaring a federal statute unconstitutional, but its permissive language providing that any party "may appeal. . . from an interlocutory or final judgment" plainly did not require the Government to appeal before final judgment was entered. Cf. United States v. Carlo Bianchi & Co., 373 U. S. 709 (1963) (review of final judgment under 28 U. S. C. § 1255 entails review of any interlocutory decisions on liability); Marconi Wireless Telegraph Co. v. United States, 320 U. S. 1, 47-48 (1943) (same); American Foreign S. S. Co. v. Matise, 423 U. S. 150 (1975) (same rule when jurisdiction based on 28 U. S. C. § 1254); Toledo Scale Co. v. Computing Scale Co., 261 U. S. 399, 418 (1923) (same).

The appellee also argues that no appeal will lie under 28 U. S. C. § 1252 because the Court of Claims did not declare an Act of Congress unconstitutional. To the contrary, a determination that the "lived with" requirement of 5 U. S. C. § 8341 (a) (3) (A) was unconstitutional was a necessary predicate to the relief the Court of Claims granted to the appellee's children, and this determination of unconstitutionality may be appealed under § 1252. McLucas v. DeChamplain, 421 U. S. 21, 30 (1975); United States v. Raines, 362 U. S. 17, 20 (1960). It is irrelevant that the Court of Claims reached this holding by relying on its earlier decision in Gentry v. United States, 212 Ct. Cl. 1, 546 F. 2d 343 (1976), rehearing denied, 212 Ct. Cl. 27, 551 F. 2d 852 (1977). An appeal under § 1252 lies for any federal-court decision declaring an Act of Congress unconstitutional in a civil action in which the United States is a party, not just for

children born out of wedlock only if they "lived with the employee . . . in a regular parent-child relationship." Such a classification based on illegitimacy is unconstitutional unless it bears "an evident and substantial relation to the particular... interests this statute is designed to serve." Lalli v. Lalli, 439 U. S. 259, 268 (1978) (plurality opinion); see id., at 279 (BRENNAN, J., dissenting). See also Trimble v. Gordon, 430 U. S. 762, 767 (1977). The Government's asserted justification for the classification-that it is an administratively convenient means of identifying children who actually were deprived of support by the employee's death-is itself open to constitutional question, since the statute does not condition benefits to legitimate children on such a showing.

It is well settled that this Court will not pass on the constitutionality of an Act of Congress if a construction of the statute is fairly possible by which the question may be avoided. E. g., Califano v. Yamasaki, 442 U. S. 682, 693 (1979); New York City Transit Authority v. Beazer, 440 U. S. 568, 582, and n. 22 (1979); Machinists v. Street, 367 U. S. 740, 749-750 (1961); Spector Motor Service, Inc. v. McLaughlin, 323 U. S. 101, 105 (1944). Where both a constitutional issue and an issue of statutory construction are raised, we are not, of course, foreclosed from considering the statutory question merely because the lower court failed to address it. Califano v. Yamasaki, supra, at 693; University of California Regents v. Bakke, 438 U. S. 265, 328 (1978)

the first such decision. Cf. Garment Workers v. Donnelly Garment Co., 304 U. S. 243, 249 (1938).

3 The lower federal courts have uniformly held that the "lived with" requirement violates the equal protection component of the Due Process Clause of the Fifth Amendment. Gentry v. United States, supra; Jenkins v. U. S. Civil Service Comm'n, 460 F. Supp. 611 (DC 1978); Proctor v. United States, 448 F. Supp. 418 (DC 1977) (three-judge court); Tenny v. United States, 441 F. Supp. 224 (ED Mo. 1977); Myers v. Commissioners of Civil Service Comm'n, Civ. No. 8682 (SD Ohio, Aug. 8, 1977).

(opinion of BRENNAN, WHITE, MARSHALL, and BLACKMUN, JJ.); id., at 281 (opinion of POWELL, J.); id., at 411-412 (opinion of STEVENS, J.). Accordingly, we turn to the statute to determine whether resolution of the constitutional question is necessary to the disposition of this case.

Shawn and Tricia Clark were denied annuities on the ground that they did not meet the statutory requirement that they "lived with the employee . . . in a regular parentchild relationship." The appellee contended that her children did meet the requirement because they had lived with the decedent as a family from their birth through 1971. If the appellee's construction of the statutory language is correct, the children are entitled to survivors' annuities and decision of the constitutional question is unnecessary. The Civil Service Commission, however, has construed the "lived with" language to require that the children be living with the employee at the time of the employee's death.

When the statutory language is considered on its face, the appellee's reading is at least as plausible as that of the Government. Shawn and Tricia had "lived with" their father, and we believe those words would not ordinarily imply a temporal limitation. Moreover, Congress has demonstrated in other social welfare legislation that it knows how to restrict the class of eligible beneficiaries to those living with an individual at a particular time.*

* See 45 U. S. C. § 231e (c) (1) (i) (Railroad Retirement Act benefits payable in certain circumstances to "the widow or widower of the deceased employee who was living with such employee at the time of such employee's death"); 42 U. S. C. § 416 (e) (Social Security Act in part defines legally adopted child as a person who "was at the time of such individual's death living in such individual's household"); 42 U. S. C. § 416 (h) (3) (A) (ii) (Social Security Act's definition of qualified child is met in part when "such insured individual is shown. . . to be the father of the applicant and was living with or contributing to the support of the applicant at the time such insured individual became entitled to benefits or attained age 65, whichever first occurred").