Garry Trudeau, the 34-year-old creator of "Doonesbury," goes on vacation from his comic strip Monday for what may be 20 months. The characters of Walden Puddle Commune--Joanie Caucus, Zonker, B.D., Uncle Duke and company--will get a rest while their author tries his hand at the arts of the musical stage and screenwriting.

Lamentations are being heard in the land, for "Doonesbury" not only reached 65 million people every day but managed to be the comic of choice of the comics-reading intelligentsia.

It vanishes at the height of its popularity. Like Charles V and Diocletian, Trudeau is withdrawing while he's ahead. Unlike Churchill, de Gaulle and Muhammad Ali, he hasn't waited to be kicked out.

According to Universal Press Syndicate, which distributes the Pulitzer Prize-winning comic strip to 720 papers, Trudeau will work on a "Doonesbury" musical in "an experimental theater workshop" with Elizabeth Swados, the avant-garde New York composer and director.

He also will complete a screenplay that he reportedly has been working on for some time, in which the main character is a leader of the New Right. The project is under the aegis of Robert Redford, who would presumably produce and direct it, according to Lee Salem of Universal Press.

Trudeau, who created "Doonesbury" for the Yale Daily News, graduated in 1970 and has been producing the seven-days-a-week comic since. He says his characters, who sprang from the social ferment of the 1960s, are now "trapped in a time warp" and he needs to "give them some $20 haircuts, graduate them and move them out into the larger world of grown-up concerns. The trip from draft beer and mixers to cocaine and herpes is a long one, and it's time they got a start on it."

Trudeau promises to be back. "It is not, repeat not, a mid-life crisis," he said in a statement.

"We have no doubt he'll be coming back to us within the time frame discussed," said Salem.

What made "Doonesbury" the most discussed political comic strip of the Watergate decade--and earned Trudeau an income estimated in the middle six figures--was a polite brand of satire that was funny, timely and squarely within bounds. Simultaneously hip, patriotic and as current as the news magazines, "Doonesbury" pointed an accusing finger (one Watergate-era strip announced John Mitchell "Guilty! Guilty! Guilty!") rather than throwing a punch.

Editorial-page artists--who have won all the other Pulitzers in the cartoon category--tend to satire and ridicule, and the best of them are capable of cruelty. The comics page is less often political, and less forgiving when it is. When Al Capp took on Joan Baez with a "Li'l Abner" figure called Joanie Phony, he lost points among the media cognoscenti. Jules Feiffer's neurasthenic figures, on the other hand, are almost too hip, reflecting a sensibility most at home in the nether reaches of Greenwich Village. Even Charles Schulz's "Peanuts" dynasty has politics: A Spockian weltanschauung played out against a background of progressive jazz.

Trudeau was the Johnny Carson of comic-strip commentators. Like Carson's "Tonight" show monologue, his strip was written close to deadline, and its goal was applause, not a call to arms. In other words, when "Doonesbury" succeeded it gave the sense that right-thinking "us" outnumbered wrong-thinking "them."

Since "Doonesbury" was a cartoon a clef, to appreciate the Trudeau slant it helped to know the real-life basis of his characters. But although Trudeau's characters are now famous, their models have become obscure. The artist may have been the only one who recognized that, but he took action nevertheless.

Earlier this month, Uncle Duke, the balding entrepreneur always pictured with sunglasses, cigarette holder and cocktail, tried to finance a movie with a cocaine deal. "I just asked myself, 'What would John De Lorean do in a situation like this?' " Duke explained. Like De Lorean, Duke was arrested.

But while John Z. De Lorean continues in the news, the life model of Uncle Duke, a writer named Hunter S. Thompson, is long gone from it. With a fake "Dr." in front of his name, trading on a reputation for drug abuse and unreliability, Thompson had been the definer and defender of "gonzo" journalism in the late 1960s. Operating from Rolling Stone magazine, he wrote drug-soaked political coverage and books with bad-boy titles such as "Fear and Loathing in Las Vegas." In the bicentennial year of 1976, when the fireplugs of Washington were painted to resemble sentimentalized cartoon figures, the fireplug at the corner of 15th and L streets NW was painted to resemble Dr. Hunter S. Thompson.

The paint has long since worn off, and few younger readers of "Doonesbury" know who Uncle Duke used to be. Furthermore, they are too busy studying torts and reading "Middlemarch" to look it up.

Lacey Davenport, "Doonesbury's" Brahmin congresswoman, was clearly patterned after Rep. Millicent Fenwick of New Jersey. The real Fenwick, who smoked a pipe and made good newspaper copy, was defeated in her bid for reelection in November.

Ace television reporter Roland Burton Hedley Jr., whose name, Time magazine proudly announced (in introducing its "Doonesbury" cover story of Feb. 9, 1976), "could have been concocted from three names on our masthead," once served as a fair satirical imitation of Dan Rather as an ambitious media man on the way up. At a time when the public had begun to notice that reporters were getting a little big for their britches, this was right on the mark. But now Dan Rather has Walter Cronkite's desk, and getting sassy with the president is out of vogue.

It was Zonker Harris of "Doonesbury" who aspired to a great tan in competitions such as the Gerald R. Ford Pro-Am Summer Biathlon Golf and Tanning contest. "Gaucho Glow" and "Alamo Sunset" were his lotions, and his inspiration the legendary tans of history: the '67 Sinatra tan, the '73 Cher tan and the '77 Andy Williams tan. A tan in the activist days of Vietnam had the dark political coloration of a college summer wrongly spent. Today, a tan once again merely means you have a place at Rehoboth. And Cher is no longer a joke, but a dramatic actress.

Zonker Harris got his name from the phrase "zonked out," a drug state which once had a certain panache. Today, however, to be zonked out is to be ranked with drunk drivers, and the citizenry is fed up with drunk drivers.

Megaphone Mark Slackmeyer had part origin in Mark Zanger, once an activist at Yale; the Rev. W. S. Sloan Jr. shared many letters of the alphabet with the Rev. William Sloane Coffin Jr., also of Yale; B.D., the "Doonesbury" character always seen in a football helmet, can be traced to former quarterback Brian Dowling, a classmate of Trudeau's at Yale. B.D. joined the Army to avoid writing a term paper. That was a hilarious reversal in the days when a student deferment was an alternative to Vietnam.

Joanie Caucus, a campaign worker who fell into bed with a reporter named Rick Redfern, has since graduated--at age 42--from Berkeley's Boalt Hall, the prestigious law school of the University of California. She and Elizabeth, a black woman who ran for office, are "Doonesbury" characters out of the National Women's Political Caucus, of which Trudeau is a member. When Joanie "graduated" in 1977, Trudeau made a rare public appearance at Boalt Hall to deliver the commencement address.

This week, Ms. Caucus had a baby by natural childbirth--as Rick giddily tried to remember how to assist with the deep-breathing exercises. It is very sweet, but it is also "Ozzie and Harriet."

Michael J. Doonesbury himself--the name is a combination of a Trudeau roommate named Pillsbury and "Doone," campus slang for a lazybones--was the pencil-nosed narrator and chronicler, the middleman, the proprietor of Walden Puddle Commune. He was Trudeau.

In its glory days, "Doonesbury" caused trouble. Occasionally a subject--Tip O'Neill or Jerry Brown or Gerald Ford or John Warner--made news by reacting publicly to his treatment, but for the most part they just wrote to ask for the original drawing, signed if possible. What kept "Doonesbury" in the news was the newspapers. Panels were periodically censored by editors whose sensitivities were offended--by sex without marriage, drugs, politics or when the subject touched home base. The Los Angeles Times, The Washington Post and the New York Daily News were among those who declined to run certain episodes.

When Time Inc. bought The Washington Star and a share of Universal Press Syndicate, "Doonesbury" left The Post and appeared in The Star under banner headlines. The Post retaliated by launching its own cartoon strip, "Dupont Circle," which had a similar flavor. When the cartoon returned to The Post, however, nobody was celebrating. It returned because The Star had died.

Garry Trudeau, eschewing celebrityhood, has not given interviews in several years. He once hid in his bathroom for three hours to avoid a reporter from The Baltimore Sun. He has done two television shows in his career. On a talk show in Boston at the age of 22, he says he was asked by his host how it felt to be "rich, famous and eligible. After staring at her in dumb panic for about five seconds, I finally just rolled my eyes." He also appeared once on "To Tell the Truth," where only one of the four panelists chose him over the two impostors. He won $167 and a pair of jade cufflinks.

His low public profile, however, has been somewhat affected by his marriage in 1980 to Jane Pauley. Pauley is seen by about 6 million people each weekday as a host of NBC's "Today" show, and her husband is a matter of fan interest. Viewers who have seen her perk up when the topic turns to babies, and who also read about childbirth in "Doonesbury," continue to put what they assume is 2 and 2 together. So far there has been no announcement of 4, however.

Trudeau's decision to take a leave of absence from his comic strip came as a shock to his syndicate and his readers, but in fact he had complained from time to time over the years about his seven-days-a-week regimen. Success, the successful often tell us, is much more limiting than failure.

In a speech to The Washington Post Book & Author Luncheon in 1971, Trudeau said of the people of the 1960s: "This generation simply has no precedent, and undoubtedly will have no successor, being a ridiculously hard act to follow."

Now the next generation has arrived, and the act Trudeau will have to follow is himself. CAPTION: Illustrations 1 through 8, Doonesbury cartoon panels Copyright (c) 1982 by G.B. Trudeau Reprinted with permission of Universal Press Syndicate. Picture, no caption