Justice Byron R. White, a former all-American halfback appointed by President John F. Kennedy to the Supreme Court, apparently is considering stepping down, sources close to the court said last week.

White's departure, whether it occurs this summer or later into President Clinton's term, would make a far greater difference on the court than would the resignation of the court's oldest member, Harry A. Blackmun, 84. Unlike White, who began as a liberal and ended up in the conservative nest, Blackmun over time has become a "liberal," holding many views the president has said he would be likely to look for in a nominee.

White's resignation would likely stunt the conservatism that began to grow in 1969, when Warren E. Burger replaced Chief Justice Earl Warren. The court's conservative penchant flowered in the 1980s and early 1990s as Presidents Ronald Reagan and George Bush named five justices and elevated William H. Rehnquist to chief in 1986.

White, 75, has said that since he came in with a Democratic administration, it would be fitting to retire under a Democratic administration. He has been on the court 31 years, still four years short of William O. Douglas's 35 1/2-year record.

People close to White say they believe he is weighing whether to retire at the end of this term, around July 1. White has not yet hired law clerks for the next term, for which work begins this summer.

"This is very late {to hire clerks}, and it would be consistent with him not to wait to step down until he was out of energy," Stanford University law professor Tom Campbell said of White -- still a strong, physically imposing man who exercises regularly and is notorious for a vise-grip handshake. Campbell, a former Republican congressman from California, was a law clerk to White in the 1977 term.

Campbell and other scholars say White's resignation would impede the power of the hard-line conservative camp, made up of Rehnquist, Antonin Scalia, Clarence Thomas and, most of the time, White, and diminish its ability to enlist the moderate-conservatives.

"Justice White may be the only Democratically appointed justice left on the court, but he is a card-carrying member of the conservative bloc," said University of Virginia law professor A.E. Dick Howard. "Even if Clinton's apppointment is moderately liberal, he or she would be a big change."

White is solidly against abortion rights. Clinton has said his nominee would not be.

White is sympathetic to government involvement with religious institutions and prayer in public schools, favoring a "low wall" of separation between church and state. Most liberal jurists are more inclined to a strict separation between church and state.

White wrote the court's 1986 opinion upholding a law against sodomy and saying the Constitution does not protect homosexual conduct. Clinton presumably would nominate a justice who shares his support for homosexual rights.

White generally opposes affirmative action, is especially tough on criminal defendants and tends to come down on the side of Congress in most disputes pitting the federal government against states or against an individual's assertion of rights.

All that could change with a liberal appointee.

"The margin on the court is generally weighted in favor of the conservatives," said Johnny H. Killian, a constitutional law specialist at the Library of Congress. "Replacing Blackmun wouldn't get you anywhere at all. . . . White's retirement would create the potential for a great deal more bargaining." Killian studies the court for the library's Congressional Research Service.

In recent terms, court rulings on the most controversial social issues of the day have been unpredictable and marked by shifting alliances. In that environment, any new justice can play an important role.

When Justice Anthony M. Kennedy joined the court in 1988, he immediately made a difference by solidifying a conservative majority. Rulings in the 1988-89 term restricted a woman's right to abortion, cut back on civil rights laws and strengthened the hand of law enforcement against criminal suspects.

Kennedy has since backed away from a consistent conservative role, possibly influenced by the 1990 addition of David H. Souter, who has adopted a more moderate approach marked by case-by-case balancing. Together with Justice Sandra Day O'Connor, they constituted a conservative-moderate coalition that determined the outcome in key cases on abortion and religion last term.

White has at times settled into the middle, becoming a critical fifth vote. In the early 1970s, when the court was split between four justices appointed by President Richard M. Nixon and four Warren court holdovers, White was a swing vote. In recent years, he has again played that role, for example, in 1990, to allow a federal judge to order a Kansas City school board to increase property taxes to pay for school desegregation, and in 1992, when the court rejected a zealous federal government sting operation that pressured a Nebraska farmer to buy child pornography.

"Justice White has the sort of views that {President Kennedy} had in the sixties," said University of Chicago law professor Geoffrey P. Miller, who was a clerk for White during the 1979 term. "He looks more conservative because the country's changed."

Miller said he "would not be surprised" if White retired at the end of the current term. "He likes to fish, walk. He's very vigorous," Miller said of White. "He's in as good of a shape as some of us are in our forties, and he has a life outside of the court."

White has been the subject of resignation rumors before, but the signals prompting the current speculation are stronger than in the past, sources said.

An assistant in White's office declined to comment on retirement speculation. The court's Public Information Officer Toni House said Friday, "I wouldn't put a lot of weight on the fact that the justice has been late hiring clerks, and the only way we know when a justice will retire is when he tells us."

White, who was born in Fort Collins, Colo., was nicknamed "Whizzer" because of his athletic ability. He was an all-American halfback at the University of Colorado. But he also excelled in academics. He was a Rhodes scholar and alternately studied law at Yale University and played professional football.

President Kennedy met White in England in 1939 when White was a Rhodes scholar at Oxford. During World War II, White served as a Navy intelligence officer in the South Pacific and wrote the official report of the sinking of Kennedy's boat, the PT-109.

After Kennedy was elected president, he made White deputy attorney general. In 1962, when a court vacancy opened, White was Kennedy's choice for the high court.