President Reagan nominated conservative U.S. Appeals Court Judge Robert H. Bork yesterday to fill a crucial vacancy on the Supreme Court, touching off what is expected to be a fierce confirmation battle over a selection that could determine the ideological direction of the court for years after Reagan leaves office.

With Bork standing by his side in the White House briefing room, Reagan said, "Judge Bork, widely regarded as the most prominent and intellectually powerful advocate of judicial restraint, shares my view that judges' personal preferences and values should not be part of their constitutional interpretations."

Democratic liberals signaled their opposition to the nomination within minutes of the announcement, some of them predicting that the nomination could trigger the most acrimonious fight since the Senate rejected two of President Richard M. Nixon's nominees for the Supreme Court in 1969-70.

"This will be the toughest fight since then because it tips the balance of the Supreme Court {and} because the president has used right-wing ideology in selecting a candidate," said Sen. Alan Cranston (D-Calif.), who also opposed both of Nixon's unsuccessful nominees.

Sen. Edward M. Kennedy (D-Mass.), a member of the Judiciary Committee, denounced the nomination unequivocally, saying that Reagan is "trying to impose his reactionary vision of the Constitution on the Supreme Court." Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) and Sen. Paul Simon (D-Ill.), another prominent liberal member of the committee -- and, like Biden, a presidential candidate -- expressed more cautious opposition.

Bork's position on abortion is likely to be a particular lightning rod for opposition to his nomination. He has described Roe v. Wade, the 1973 Supreme Court decision legalizing abortion, as "unconstitutional."

White House spokesman Marlin Fitzwater said "we recognize that any conservative would receive some opposition, but we believe that Mr. Bork will be confirmed." Another senior White House official predicted a "tough and lengthy" fight but said he is confident that the administration can muster the 60 votes needed to stave off a Democratic filibuster and win Bork's confirmation before the Supreme Court reconvenes in October.

Reagan named Bork, 60, who serves on the U.S. Court of Appeals for the District of Columbia Circuit, to replace Justice Lewis F. Powell Jr., 79, a 1971 Nixon appointee who resigned last week for health reasons. While the administration went through the formality of consulting Senate leaders in advance, officials said that Bork was Reagan's choice from the outset and was also favored by Attorney General Edwin Meese III and White House chief of staff Howard H. Baker Jr.

While Republican members of the Senate Judiciary Committee lined up solidly behind Bork, ranking Republican Strom Thurmond (S.C.) said he was disappointed that Reagan had not named another southerner to replace Powell.

Thurmond, who supported William M. Wilkins, a federal appeals judge from South Carolina, met privately with Reagan yesterday. Afterward, a senior official said that there is "a possibility" that Wilkins will nominated to be director of the Federal Bureau of Investigation. The post has been vacant since William H. Webster was confirmed May 19 as director of central intelligence.

The nomination of Bork produced jubilation among conservative activists, consternation among civil-rights and pro-abortion groups and words of caution from moderate Republican and conservative Democratic senators.

"I think he will have the most complete and exhaustive investigation of any nominee to the Supreme Court in history," said Sen. Howell T. Heflin (D-Ala.), the committee's most conservative Democrat.

The votes of Heflin and another relatively conservative Democrat, Sen. Dennis DeConcini (Ariz.) could play a key role in the outcome of the confirmation battle. Both said they have "an open mind" about Bork.

But in an extraordinarily sharp statement, Kennedy accused Bork of advocating "an extremist view of the Constitution" and of harboring "neanderthal" views on civil rights and the First Amendment. He said Bork's willingness to carry out "the unconscionable assignment" of firing special prosecutor Archibald Cox during the Watergate scandal is grounds to disqualify him for appointment to the Supreme Court.

"Robert Bork's America is a land in which women would be forced into back-alley abortions, blacks would sit at segregated lunch counters, rogue police could break down citizens' doors in midnight raids, schoolchildren could not be taught about evolution, writers and artists could be censored at the whim of government and the doors of the federal courts would be shut on the fingers of millions of citizens . . . , " Kennedy said.

He added that Reagan "should not be able to reach out from the muck of Irangate, reach into the muck of Watergate and impose his reactionary vision of the Constitution on the Supreme Court and on the next generation of Americans."

Typical of the enthusiasm the nomination generated among conservatives was the endorsement of New Right activist and fund-raiser Richard Viguerie. "Conservatives have waited for over 30 years for this day," he said. "This is the most exciting news for conservatives since President Reagan's reelection."

Even before Reagan made the announcement, civil-rights and pro-abortion groups were mobilizing to block Bork, focusing in particular on his opposition to affirmative action and abortion. Powell, a frequent swing voter, cast the decisive votes in two Supreme Court cases last year that disappointed the administration by upholding women's right to abortion and affirmative-action remedies to rectify racial discrimination.

In 1981 testimony before a Senate Judiciary subcommittee, Bork said he was convinced that the Supreme Court's landmark 1973 decision approving abortion, Roe v. Wade, was "an unconstitutional decision, a serious and wholly unjustifiable judicial usurpation of state legislative authority." Opponents of abortion are hopeful and pro-abortion groups fearful that Bork would attempt to reverse this decision.

Expressing his philosophy on the role of judges, Bork said in a 1984 lecture: "In a constitutional democracy, the moral content of law must be given by the morality of the framer or the legislator, never by the morality of the judge. The sole task of the latter -- and it is a task large enough for anyone's wisdom, skill and virtue -- is to translate the framer's or the legislator's morality into a rule to govern unforseen circumstances."

Both sides in the debate on Bork's confirmation see his appointment as an opportunity to shape the decisions of the court for decades.

Daniel J. Popeo, founder of the conservative Washington Legal Foundation, said, "We have the opportunity now to roll back 30 years of social and political activism by the Supreme Court. The activists who have used the Supreme Court as a vehicle for political and social change instead of the ballot box are in big trouble."

Popeo said Bork's confirmation would "guarantee that capital punishment statutes are going to be upheld, that Roe v. Wade is in jeopardy and that certain affirmative- action quota cases may be looked at a little differently."

Benjamin Hooks, executive director of the NAACP, and Ralph Neas, executive director of the Leadership Conference on Civil Rights, said on behalf of the conference "that a very substantial majority of the civil-rights community will strongly oppose the nomination of Robert Bork."

Hooks and Neas said Bork's confirmation would "jeopardize the civil-rights achievements of the past 30 years. Well-established law on affirmative action, on privacy, on women's rights and on school desegregation could overnight be substantially eroded or overturned."

Reagan and other administration officials sought to play down ideological considerations yesterday, stressing instead Bork's legal qualifications, which are not disputed. The president called him "a premier constitutional authority" with "unrivaled scholarly credentials." He noted that when Bork was confirmed as an appeals court judge in 1982, the American Bar Association gave him its highest rating, "exceptionally well qualified."

In the hearings on his appointment to the appellate court, Bork survived an examination of his controversial role in the "Saturday Night Massacre" of 1973 in which he fired Cox as Watergate special prosecutor after two higher-ranking officials resigned rather than do so. One of these officials, then-Attorney General Elliot L. Richardson, endorsed Bork this week and said he behaved properly in dismissing Cox. But several Democrats said that Bork's role in the affair will be reexamined.

Senate Majority Leader Robert C. Byrd (D-W.Va.) said both the president and the Senate are entitled to use "ideological standards" in making their judgments on court nominees. But Heflin said he doubts that Bork could be rejected simply because of his conservatism.

While Republicans said they will press Biden to expedite committee hearings and hope that Bork is confirmed by the start of the next Supreme Court term, several Democrats said the confirmation process could stretch into November and beyond. Byrd warned that if Republicans continue "this binge of stalling and delay" on legislation they oppose "I'll play a little of this hard ball in calling up the nomination" to the Senate floor.

GOP members of the Judiciary Committee praised Bork's qualifications and warned that attempts to delay the confirmation process would backfire on the Democrats. "You can play a little bit of politics for a while, but it will wear very thin with the public at large," said Sen. Orrin G. Hatch (R-Utah).

Staff writers Howard Kurtz and Ruth Marcus contributed to this report.