Three conservative Republicans -- federal appeals court Judges Robert H. Bork and J. Clifford Wallace and Utah Sen. Orrin G. Hatch -- emerged yesterday as the leading candidates to replace retiring Justice Lewis F. Powell Jr.

All three men share a philosophy of judicial restraint in line with the Reagan administration's distaste for activist judges. If nominated and confirmed, any of them would likely be far more conservative than Powell, for years a swing vote between the court's precariously balanced liberal and conservative wings.

Powell's announcement that he was retiring after 15 year on the nation's highest court surprised the White House. And the short list of candidates being discussed by lawyers, lobbyists and government officials yesterday was a tentative, fast-changing assortment of conservative names.

Also mentioned as possible successors were a number of Reagan appointees serving on federal appeals courts: Richard A. Posner and Frank H. Easterbrook of Chicago, two leading advocates of the controversial law-and-economics school of legal thought; Patrick E. Higginbotham of Dallas; Ralph K. Winter of New Haven; and Pasco Bowman of Kansas City.

Topping almost everyone's list yesterday were Bork and Hatch, with Wallace a frequently mentioned third possibility.

Bork, 60, is a highly regarded conservative named by Reagan to the D.C. Circuit Court in 1982 but passed over for nomination to the high court last year in favor of his colleague, Antonin Scalia. As U.S. solicitor general during the Nixon administration, he fired Watergate special prosecutor Archibald Cox during the "Saturday Night Massacre" after two higher-ranking officials refused to do so -- an issue that would be certain to come up in confirmation hearings.

Bork's age may also work against him in an administration committed to shaping the federal judiciary for years to come.

In a speech in 1985, Bork espoused the Reagan administration's view that faithfulness to the "original intent" of the Constitution's framers "is the only legitimate basis for constitutional decision" and "essential to prevent courts from invading the proper domain of democratic government. The Constitution, he said, does "not cover all possible or even all desirable liberties."

In a controversial 1984 ruling, Bork -- on behalf of a three-judge panel -- found that the Navy was justified in dismissing a sailor for homosexuality. Bork found that there is "no constitutional right to engage in homosexual conduct and that, as judges, we have no warrant to create one," implicitly questioning the Supreme Court's decision that abortion rights are protected by the constitutional right to privacy.

Hatch, 53, the Reagan administration's staunch champion on Capitol Hill of issues ranging from civil rights to the Iran-contra affair, serves on the Senate Judiciary Committee, which will scrutinize the nominee to replace Powell. Although Hatch would enjoy the benefits of senatorial courtesy if his colleagues were called on to consider his nomination to the high court, he would also draw heavy fire from civil rights activists and other liberal groups who have been engaged in fierce battles with him over the years.

"If the administration thinks that the easy way out is to name a sitting senator and that senator is Hatch, I think they'd be in for a very big surprise," said Art Kropp, executive director of the liberal People for the American Way. "Hatch will be controversial, and he will be opposed and it will not be smooth sailing. I can almost guarantee that."

Hatch's nomination could also be complicated by a constitutional provision barring members of Congress from being named to any office "the emoluments whereof shall have been increased" during their terms. Supreme Court justices this year received a $6,000 pay raise to $110,000 -- an increase that some legal experts believe could doom his ability to serve on the high court. Hatch supporters say the matter could be easily remedied by passing a bill cutting the salary for his seat.

Wallace, 58, who has served since 1972 on the 9th Circuit Court of Appeals in San Diego, is a devout Mormon. He has said that the Bible provides "great scriptural support for the death penalty," questioned the need for "a wall between state and religion" and warned, "I don't think the Constitution was developed to answer all questions or cure all social ills."

Well-regarded by the Californians who are among Reagan's closest advisers, Wallace was a leading contender for the vacancy created by the late Justice Potter Stewart's retirement in 1981 -- a seat that went to a little known Arizona state court judge, Sandra Day O'Connor. President Gerald R. Ford also considered Wallace for the late Justice William O. Douglas' seat, for which he eventually nominated Justice John Paul Stevens.

The search for Powell's successor is colored by the fact that the vacancy has occurred late in Reagan's presidency; at a time when the administration is reeling from the disclosures of the Iran-contra affair, which has eroded its influence in Congress; and -- unlike Reagan's two previous nominations -- while the Senate is controlled by Democrats.

As a result, the administration is under pressure to choose a candidate who will not create a firestorm of opposition on Capitol Hill. Last year, 33 senators voted against confirming William H. Rehnquist as chief justice; only 41 are required for a filibuster to block a nomination.

Duke University law Prof. Walter Dellinger called Bork "the most likely candidate" and said it would "be very difficult" to block his confirmation.

"I don't think there's any guarantees in life, but I think that if they go with Bork or Hatch that these are individuals that it's difficult" to block, said Patrick B. McGuigan of the conservative Free Congress Foundation. "It would be difficult for the other side credibly to oppose Bork, and with Orrin you have the collegiality factor at work.

"I'll be very surprised if it's anybody else," McGuigan added. "The consensus breaks down totally after those two among analysts on the outside, both liberal and conservative, and I suspect within the administration."

However, neither man would sail through the Senate unopposed.

"I think you're going to see a very definite change" from the Rehnquist-Scalia hearings last year, said a Republican source. "Anything's possible at this point. It's difficult to handicap how this is going to go."

With the nominee replacing a justice who has played a pivotal role as a swing vote on many issues rather than one who is consistently conservative, liberal senators may have more ammunition to argue that it is legitimate to consider the nominee's ideology and potential for tipping the balance of the court.

"Here you're not replacing one right-wing justice, you're replacing a moderate swing vote, and that will come into play in the decision," said Nancy Broff, director of the Judicial Selection Project at the Alliance for Justice, a liberal lobbying group.

Nan Aron, director of Alliance for Justice, another liberal lobbying group, said Bork's confirmation "would not be as easy as some people feel. Bork is a guy who's an advocate of free-market libertarianism, and there would be a lot of concern about the way he'd apply and interpret the Constitution."

Aron said Hatch would be "the hardest nominee to defeat because he is a member of the club." But she said Hatch has hurt his credibility with his passionate defense of the administration during the Iran-contra hearings.

Another complicating factor involves regional loyalties. South Carolina Sen. Strom Thurmond, the Judiciary Committee's ranking Republican, said yesterday that he believes it is important to have a southerner on the court. The departure of Powell, a Richmond area native, leaves the court without one.