A defiant Robert H. Bork, saying he harbors "no illusions" that he will be approved by the Senate, vowed nonetheless yesterday to continue his fight for confirmation to the Supreme Court "for the sake of the federal judiciary and the American people."

Displaying emotion that he had not revealed during five days of testimony before the Senate Judiciary Committee, Bork said he is the victim of a "disturbing" and "dangerous" lobbying campaign that endangers the independence of the judiciary.

"A crucial principle is at stake," Bork said in a dramatic appearance in the White House briefing room. "That principle is the way in which we select the men and women who guard the liberties of all the American people. That should not be done through public campaigns of distortion. If I withdraw now, that campaign would be seen as a success and it would be mounted against future nominees." {Text of statement, Page A10.}

Bork has been opposed by a broad coalition of civil rights, environmental and women's groups that have waged an aggressive and apparently successful campaign against his nomination. His conservative supporters have taken out newspaper ads and generated thousands of letters and phone calls to Congress, but have generally spent far less and been less visible, partly at the suggestion of White House strategists.

President Reagan's "choice of Robert Bork made this a political fight," said Nan Aron, executive director of the Alliance for Justice, an anti-Bork group. "The selection of judges has always had an element of politics -- a point not lost on President Reagan when he named Robert Bork to the Supreme Court," she said.

The prevailing view at the White House and on Capitol Hill was that Bork's statement, issued after a meeting with Reagan and his senior advisers, will not affect the outcome in the Senate, where 53 senators have said they will vote against confirmation. Thirty-seven senators have declared for Bork, and 10 others have not announced how they will vote.

The president issued a written statement immediately after Bork's appearance, saying that he was "pleased by Judge Bork's decision to go forward with his nomination for the Supreme Court" and denouncing his opponents for what he labeled "an attack based on innuendos, mistruths and distortions."

But Reagan did not appear with Bork in the briefing room, and one White House official said that Bork's decision had "complicated the strategy" of filling the Supreme Court vacancy created by the retirement of Lewis F. Powell Jr. The official observed that Reagan on Thursday had said that "Bork had a decision to make," a formulation the president has used in the past when an administration appointee was under fire and about to withdraw. Bork "took the president's statement literally," the official said.

Vice President Bush said in an interview with Cable News Network that the only reason Reagan did not accompany Bork was that the president "was going off to Camp David." Reagan departed a half hour after Bork's statement, pausing for a moment on the helicopter steps to tell cheering Bork supporters assembled on the White House lawn "that we are going to fight on for an independent judiciary, and we'll stay in the fight and see that we get our story told."

The Bork supporters, carrying signs that read "America wants Bork" and "We have just begun to fight," had gathered earlier in the afternoon on the Ellipse, where Rep. Jack Kemp (R-N.Y.), a Republican presidential candidate, told them that he would be "proud" to renominate Bork if he is not confirmed.

Attorney General Edwin Meese III issued a statement fully supporting Bork's decision. But White House officials, citing Bork's own statement that he did not have illusions about winning, said the administration was free to seek an alternative nominee that could quickly be presented to the Senate if Bork is rejected, and Justice Department officials said the search for a successor is continuing. Asked if Justice officials are updating files and conducting research on alternative choices, one department official said, "You bet."

Friends of Bork said that he wrestled with the decision of whether to withdraw since the Judiciary Committee voted 9 to 5 last Tuesday to send his nomination to the Senate with an unfavorable recommendation. One source close to Bork said that and his wife, Mary Ellen, were "moved" by pleas from Senate supporters at a meeting Wednesday that he should refuse to withdraw. The source said this reinforced "Bob Bork's basic impulse not to quit."

Sen. Alan K. Simpson (R-Wyo.) made what one participant in the meeting described as a "particularly eloquent" plea for Bork not to withdraw. Simpson said yesterday, "If I were involved, if I'd spent a good part of my life building a fine reputation, with 5 1/2 years on one of the nation's most respected courts, consistently joined in opinions by thoughtful people on that court, if I'd been solicitor general of the United States and compiled an honorable record, I'd want to go tell my story even if I lost. If you lose, what the hell risk is that?"

White House chief of staff Howard H. Baker Jr. said that Bork, who was in seclusion Thursday writing his statement, did not tell Reagan of his decision before he came to the White House. "His decision was very characteristic of Judge Bork," Baker said. "He's determined, he's courageous and the president is with him all the way."

The timetable for the Senate debate on Bork's confirmation was not immediately clear. An aide to Sen. Strom Thurmond (R-S.C.), ranking Republican on the Judiciary Committee, said the minority report on the Bork confirmation hearings could be filed as early as next Tuesday.

Senate Majority Leader Robert C. Byrd (D-W.Va.) said he will bring the nomination to the Senate floor after the committee report is available.

"It is in the interest of Mr. Bork and the country that the {court} vacancy be filled as soon as possible," he said.

The Bork debate, however, is certain to slow other Senate business and could further jeopardize the Nov. 21 target date for congressional adjournment. Byrd indicated earlier that if a new nominee is sent to the Senate quickly, he would hold the Senate in long enough for a confirmation vote.

Bork's defiant announcement caught the Senate by surprise. Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) was in California and his staff had been preparing to release a written statement on Bork's expected withdrawal that had to be scrapped.

Senate Republicans rushed to praise Bork's decision, which Minority Leader Robert J. Dole (R-Kan.) called "a rather courageous thing to do."

"He's entitled to a debate," Dole said. "He's entitled to have some reasonable debate on this Senate floor, not personal attacks and questions of who has the slickest advertising."

Dole said some may view Bork's decision as "foolish," but that "maybe he'll keep his reputation intact, maybe by his example we'll have better people in government."

"The odds in this case are probably unbeatable," he said. "Probably. There is always some hope."

Bork's chances of winning confirmation, however, seemed as hopeless after the announcement as they did earlier in the week. Sen. David F. Durenberger (R-Minn.) announced yesterday that he will support Bork, reducing to 10 the number of uncommitted votes.

None of the 53 senators who have committed publicly to vote against confirmation was considered likely to switch sides in such a highly visible and politically charged fight.

After his remarks, Dole and Sens. James A. McClure (R-Idaho) and Jesse Helms (R-N.C.) telephoned Bork from the Senate cloakroom, reaching him in a car as he was leaving the White House. Dole was quoted as saying, "We're ready to do battle."

"We're all delighted," Helms said. "You have served your country well."

Bork's decision was also supported by Senate Majority Whip Alan Cranston (D-Calif.) and Sen. Arlen Specter (R-Pa.), the only Judiciary Committee Republican to oppose confirmation.

"Some of Bork's supporters, including President Reagan, have railed about lynch mobs and character assassination," Cranston said. "I totally reject this . . . . I believe the Senate debate will demonstrate to the American people the wisdom of the majority of senators in their decision to reject Judge Bork."

Specter said he agreed with Bork's assertion that "unfair charges have been made against him" and that he shared Bork's hope that "voices will be lowered." However, there were indications that the floor debate could be bitter.

"Talk about arrogance," Sen. Dale Bumpers (D-Ark.) said on the Senate floor after Bork's announcement. Bumpers said Bork faced certain defeat because senators studied his testimony and earlier writings. "I can tell you that before Judge Bork testified, he would have been confirmed," he said.

"I am not one who is going to be intimidated by people talking about a lynch mob," Bumpers said.

Sen. Orrin G. Hatch (R-Utah), one of Bork's strongest supporters, said he expected three days to a week of debate on the nomination.

"Some of those who distorted his record will have to stand up on the floor and take the medicine for their distortions," Hatch said.

Interviewed on "John McLaughlin's One on One," Treasury Secretary James A. Baker III provided a political perspective of what had happened. He said the confirmation "became purely and simply a political fight . . . and we lost control of the Senate in 1986, and therefore, I think it was extremely difficult for us to win."Staff writers Dale Russakoff, Ruth Marcus and Al Kamen contributed to this report.