President Reagan, backing away from another confrontation with the Senate, struck a conciliatory note yesterday as he nominated federal appeals court Judge Anthony M. Kennedy of Sacramento to fill the critical vacancy on the Supreme Court.

"The experience of the last several months has made us all a little bit wiser," Reagan said in reference to the controversies surrounding his two previous attempts, both unsuccessful, to fill the swing seat on the court vacated June 26 when Lewis F. Powell Jr. retired.

Kennedy, 51, is the president's third choice for the seat. Last month, the Senate rejected Reagan's first choice, Judge Robert H. Bork, on a 58-to-42 vote. Judge Douglas H. Ginsburg, the president's second nominee, withdrew Saturday after disclosures that he had used marijuana while a law professor at Harvard.

Senate reaction to Kennedy's nomination was generally favorable, but the enthusiasm was muted by the troubles encountered by Ginsburg and Bork. Most senators said the nominee can expect intense scrutiny. {Details, Page A37.}

Appearing before reporters in the White House briefing room, Reagan called Kennedy "a true conservative," praised his record on the bench and in civic affairs and described him as a "courageous, tough but fair jurist."

The president appealed for a "spirit of cooperation and bipartisanship" in the confirmation hearings on Kennedy, which are expected to begin in January. For his part, Reagan refrained from the confrontational rhetoric of his statement nominating Ginsburg, when he denounced the Senate for first delaying hearings on the Bork nomination and then yielding to "a campaign of pressure politics" against him.

White House officials said administration officials grilled Kennedy for three hours on Sunday and that FBI agents talked to him for 10 hours in an effort to prevent repetition of the political embarrassment the Ginsburg nomination caused the administration.

A senior official said Reagan himself asked Kennedy, during a half-hour meeting in the White House residence on Monday evening, whether there is anything in his background that could jeopardize confirmation, and was told there is not. The official said White House deputy chief of staff Kenneth M. Duberstein asked the same question of Ginsburg before he was nominated but that Ginsburg said nothing about marijuana use.

Kennedy told reporters that he had been asked specifically whether he had ever used marijuana and said, "The answer was no, firmly no."

Significantly, Kennedy was accompanied to the White House briefing room by two congressional supporters from his state, Democratic Rep. Robert T. Matsui and Republican Sen. Pete Wilson. Matsui, an attorney who has known Kennedy for 30 years, said Kennedy's judicial outlook is similar to Powell's and called him "the best appointment that the president could be expected to make."

Wilson also praised Kennedy and said he "could not conceive of opposition to him" from conservative Republican Sens. Orrin G. Hatch (Utah) or Jesse Helms (N.C.). Hatch has sharply criticized the White House for withdrawing Ginsburg's nomination. And Helms once threatened to filibuster against Kennedy's confirmation.

Addressing a Republican group in New Jersey on Oct. 13, before the Senate's vote on Bork but after it was clear that the nomination would be rejected, Reagan had promised angrily to find another nominee "that they'll object to just as much as they did . . . this one." When the president was asked yesterday about that comment, he said it was a "facetious remark" that he shouldn't have made.

Kennedy also took a different tack yesterday from Reagan's two previous choices for the Powell seat. When Bork was nominated, he stood stonily alongside Reagan and refused to answer questions. After Ginsburg was nominated before an audience of conservative supporters, he predicted that he would be confirmed.

In contrast, Kennedy, a former Sacramento lobbyist, said he was "delighted" to be nominated, even as a third choice, and stressed the "constitutional obligation" of the Senate to scrutinize court appointments.

"I share with you, Mr. President, and with each member of the Senate an abiding respect for the Supreme Court, for the confirmation process and for the Constitution of the United States. . . , " he said.

Kennedy, a graduate of Stanford University and Harvard Law School, practiced law in San Francisco and Sacramento before being named to the appeals court by President Gerald R. Ford in 1975, at age 38. The son of a prominent Sacramento lawyer, he lobbied in Sacramento on behalf of distillers, optometrists and others, acquiring, he told an interviewer several years ago, "a faint contempt for the legislative process."

While in private practice, Kennedy helped then-Gov. Reagan draft Proposition 1, his tax-limit initiative defeated in 1973. Reagan and his chief aide, Edwin Meese III, now the attorney general, backed Kennedy for his nomination to the appeals court.

In his more than 400 opinions as a judge, Kennedy has generally adopted a conservative approach on criminal law, civil rights and other issues, but has not engaged in the wide-ranging criticism of Supreme Court precedents that characterized Bork's opinions and writings.

Among his best-known rulings are decisions finding the legislative veto unconstitutional, overturning a lower court decision requiring Washington state to pay male and female employes based on the "comparable worth" of their jobs, and upholding the Navy's firing of homosexual sailors. He also upheld capital punishment in several rulings, as did Powell.

The White House strategy in pushing Kennedy's confirmation is to stress his judicial qualifications, as administration officials did with Bork, and his position on criminal justice issues, as Reagan attempted to do with Ginsburg.

But Bork's indisputably strong legal qualifications became subordinated to concerns that he would be a judicial activist who would undo previous high court rulings on civil rights, abortion and other social issues. The campaign for Ginsburg never got off the ground before he withdrew, but he had almost no experience in criminal justice cases.

Kennedy, however, has both judicial experience and a track record on criminal justice issues. Reagan emphasized both points yesterday and said "the Constitution established a system of criminal justice that not only protects the individual defendants but that will protect all Americans from crime as well."

Kennedy's nomination is a measure of vindication for White House chief of staff Howard H. Baker Jr., who had supported him when Meese was recommending Ginsburg. But Reagan defended Meese yesterday. The president denied that the Justice Department "blew" the Ginsburg investigation, and he left the briefing room with an arm around Meese's shoulders.

Baker was told yesterday morning by the Federal Bureau of Investigation that a preliminary check turned up nothing negative on Kennedy. The court post was then offered to Kennedy by the president. Reagan said, however, that he will get the results of a complete FBI background investigation before formally submitting Kennedy's name to the Senate.Staff writer Ruth Marcus and staff researcher Michelle Hall contributed to this report.