President Reagan's colorful conservative watchdog, Lyn Nofziger, bowed out in a shower of jellybeans yesterday at a barb-filled and nostalgic White House briefing that may also have marked a significant turn in administration strategy.

Asked why he was jumping ship, Nofziger said, "It's probably my rat heritage." What he will miss the most in private life, added the irreverent aide, is "the bathroom in my office."

It was vintage Nofziger, though not equal to the quips Nofziger makes away from the briefing podium. Recently, the California newsletter The Political Animal quoted him as saying of Reagan: "He's half a disciple of Ben Franklin. He believes in early to bed."

At the briefing yesterday Nofziger jested that the biggest change he had noticed in Reagan in the past year was that "he has gone from 56 to 70." He said soon thereafter that he "wasn't trying to make any inferences that there is anything there except just the passage of time."

Nofziger's sense of humor as well as his unrestrained ideological conservatism put him in near-constant hot water during the 1980 campaign and much of his one uneasy year as Reagan's political aide after the election.

His departure is a source of concern to conservatives who are critical of the administration and considered Nofziger their most dependable spokesman inside it.

Speaking of Nofziger's role in fighting for conservative appointees, New Right fund-raiser Richard Viguerie said of him last year, "Lyn manned the barricades and did the work of the Lord."

But Nofziger lost at least as many battles as he won. He was isolated in the Executive Office Building, where he used the working office once preferred by Richard M. Nixon, whose autographed picture Nofziger prominently displayed.

In California, especially during Reagan's first campaign for governor in 1966, Nofziger was a leading Reagan aide and confidant. In Washington, he reported to the president through White House chief of staff James A. Baker III, a pragmatist who had previously worked for Gerald R. Ford and George Bush.

Nofziger did not conceal his disdain for this arrangement or for what he considered the political timidity of the White House staff. Yesterday, betraying a well-nourished weakness for bad puns, Nofziger referred to the White House handling of the tax exemption for segregated schools as "botchulism." While lavishly praising Reagan, Nofziger also again criticized the administration's appointments process.

"I think in some cases we've brought in people who really didn't want the president in office and who really don't agree with what he wants to do, and I just disagree with those who felt it was proper to put that kind of person there," Nofziger said.

Nofziger, 57, who is leaving to open a consulting business here, said he thought Reagan ultimately would satisfy most of his conservative critics, but praised the pressures his ideological friends are now putting on the administration as "healthy and helpful." Some administration officials say they believe it will be more difficult to contain those pressures with Nofziger gone.

The cigar-chomping Nofziger was never part of the high style the Reagan administration brought to Washington. He said he liked to drink more than the Reagans did, and he was openly contemptuous of the black-tie dress required at many administration social functions.

In California he once responded to a criticism Nancy Reagan supposedly had made of his attire by saying that Reagan looked "that much better" standing next to him.

Nofziger's low point during the 1980 campaign probably occurred during an interview with David Bundy of The Sunday Times of London, which Nofziger thought wasn't likely to show up in the United States.

Objecting to rumors Nofziger said that Carter aides had started about Reagan, Nofziger told Bundy: "Now, I'm going to start another rumor. Jimmy Carter has the clap."

The story was carried on the Los Angeles Times-Washington Post News Service, and appeared in many U.S. papers.

But when Reagan was wounded by a would-be assassin's bullet last March 30, it was Nofziger who calmly relayed information and Reagan one-liners to the media without betraying his emotions.

That performance was recalled by several aides yesterday, as well as by reporters, who affectionately tossed jellybeans at Nofziger when he had finished the White House briefing. In times of crisis Reagan had no stauncher aide.