For 15 years as a federal appeals court judge, Samuel A. Alito Jr.'s job has been to follow the precedent of the Supreme Court. But if he is approved for the nation's highest court, he would not have to.

As one of the nine final arbiters of American law he could vote to overturn long-standing decisions on abortion, affirmative action and religion -- with nothing to stop him except stare decisis, the legal principle that, for the sake of stability, courts should generally avoid undoing their past rulings.

But Alito's associates and independent legal analysts who know his record say a Justice Alito would be reluctant to use that power, even in such areas as abortion, in which the court's past rulings are most controversial.

"If he learned anything from me, he learned the value of stare decisis," said Judge Leonard I. Garth, a Nixon appointee on the U.S. Court of Appeals for the 3rd Circuit for whom Alito, 55, served as a law clerk in 1976-77 -- and later joined as a colleague on the court.

But Garth added: "If what you're thinking is 'Would Sam overrule Roe?' -- he would not. He might have restrictions and limitations, but it is a precedent he'd honor. As a previous mentor and as a present colleague, I don't think he'll overrule it."

If that assessment proves valid, Alito would not be in the mold of Justice Clarence Thomas, the court's most conservative member, who has advocated revisiting a wide range of past cases he views as inconsistent with the Constitution. Nor would he be a carbon copy of conservative Justice Antonin Scalia, who has fewer quarrels with established doctrine than Thomas does, but who would overrule Roe v. Wade, the 1973 abortion-rights decision.

Liberal critics of the Alito nomination are skeptical. They note Alito once interpreted an ambiguous Supreme Court precedent to uphold a Pennsylvania law that a married woman must notify her husband before getting an abortion. And they say that President Bush named the Yale Law School graduate after his first choice, White House counsel Harriet Miers, withdrew under fire from social conservatives.

"I think they are honestly trying to find someone who will overturn Roe v. Wade, and the history of the Miers nomination shows that," said Marcia Greenberger, co-president of the National Women's Law Center, which supports abortion rights.

Unquestionably, the power to reverse precedent is among the most awesome the court possesses, as the court itself has often recognized.

In reaffirming Roe in 1992 by a 5 to 4 vote, the Supreme Court relied heavily on stare decisis. The court said that even if the decision was not perfect in its original form, reversing its essential holding would be too disruptive to a society accustomed to thinking of abortion as a right.

Nevertheless, the court has shown that stare decisis is not an inviolable command. The 1954 Brown v. Board of Education decision ordered school desegregation, striking down the "separate but equal" rule the court had established in Plessy v. Ferguson 58 years earlier.

And in 2003, the court struck down all state laws against private consensual sodomy, explicitly overruling its 1986 decision that said states could criminalize homosexual acts.

Judiciary Committee Chairman Arlen Specter (R-Pa.) asked Alito about stare decisis during their informal meeting last week. Specter said that the nominee has told him he would evaluate precedent on a "sliding scale," giving the greatest weight to decisions that had been upheld by a large number of different justices appointed by different presidents.

Specter did not ask Alito directly about Roe. Nor did Alito address Specter's suggestion that some long-settled cases acquire "super-precedent" status. But the chairman said in an interview that "these questions are valuable because if . . . you work the edges and fringes, you can then try to get a feel for not just the words but the music -- the body language and the demeanor."

Alito's concept of a "sliding scale" is interesting in light of abortion-rights history: In the Supreme Court's 1992 decision upholding Roe, four of the five votes came from justices who were put on the court after Roe was initially decided.

John Paul Stevens was appointed by President Gerald R. Ford. Sandra Day O'Connor and Anthony M. Kennedy were appointed by President Ronald Reagan. David H. Souter was appointed by President George H.W. Bush. The fifth vote came from Roe's author, Harry A. Blackmun, appointed by President Richard M. Nixon.

Those who know Alito well say he would treat precedent respectfully in part because that is what he has done for years on the 3rd Circuit, which is based in Philadelphia.

"Based on my experience, he has an abiding respect for stare decisis, and frankly I've never seen anything that would give rise to a hint of disrespect for precedent," said Timothy K. Lewis, a Washington lawyer who served on the 3rd Circuit from 1992 to 1999. "He is unequivocally not a judicial activist in any way, shape or form."

"Once he's confirmed, is he going to go off on creative jaunts, or instead is he going to rely on prior Supreme Court precedent almost as much as he relied on it as a circuit judge?" asked David Garrow, a Supreme Court historian at Cambridge University in Britain who has been studying Alito's appeals court opinions. "The likely behavioral answer is that, having done things one way for 15 years with absolute consistency, he'll continue to largely do things that way."

Jeffrey Wasserstein, a former Alito law clerk who said he voted for the Democratic presidential ticket in 2004, said: "He recognizes that precedent underlies our system and that it is necessary for settled expectations. I'd be personally surprised if he lightly overruled a precedent that has been on the books for 30 years."

Abortion rights advocates say Alito's 1991 dissenting opinion upholding the Pennsylvania spousal notification statute showed he was willing to push the law in the direction of his own policy preferences.

He was a minority of one on a three-judge panel, and the majority's view was sustained by the Supreme Court.

But lawyers who know him, noting that his opinion avoided any wider criticism of Roe, see it as his best effort to interpret a murky standard that had been laid out by O'Connor in some previous cases.

"Alito was trying to understand what O'Connor meant," said Howard Bashman, a Philadelphia appellate lawyer who has argued before Alito. "But now she's said what she meant."

Bashman recalled one civil rights case in which he represented a prisoner with a highly technical claim on which other appeals courts had reached varying rulings. Alito recognized that the issue was controlled by an existing 3rd Circuit precedent, and dismissed the appeal in what Bashman called "a quick opinion saying they were bound by the prior panel's opinion. He was not out trying to stir up a hornet's nest."

Though Alito's rulings on the 3rd Circuit have generally reached conservative results, he has not publicly articulated an overarching critique of recent Supreme Court jurisprudence.

This is in contrast not only to Scalia and Thomas, but also to other federal judges Bush might have chosen.

As a law professor, Michael W. McConnell, who now sits on the U.S. Court of Appeals for the 10th Circuit in Denver, attacked Roe and developed a theory on the relationship between church and state. As a member of the California Supreme Court, Janice Rogers Brown, now on the U.S. Court of Appeals for the District of Columbia Circuit, denounced Supreme Court precedents giving commercial advertising less constitutional protection than political speech.

"He is not coming from the academic perspective of someone who's looked at and criticized the Supreme Court from a theoretical perspective," Wasserstein said. "He is someone who, for his entire career, he's looked at the practical applications of constitutional law."