THE MUSICAL adaptation of "Doonesbury" won't add flesh to the figures of your fantasies. In fact, Doonesbury and company, so sensitively shaded in newsprint, are somehow more cartoonish in three dimensions. The show is likable and loud, but disappointingly simple-minded for the offspring of a comic strip that has kept more than one president on his toes.

"Doonesbury" is careful to touch on all the trendy issues: feminism, the freeze and Fonda fitness ("it firms you up as it develops your political sensitivity"), but there's a sense that creator Garry Trudeau is talking down to this audience, rather than making them co-conspirators as he does with his daily readers. Trudeau has pulled his punches, and this "Doonesbury" has few real jabs and insights, relying instead on facile lifts from pop culture and personality magazines. The result is a sort of "You're a Good Man, Charlie Brown" for grown-ups.

Trudeau and director Jacques Levy set up a silly sitcom situation. It's graduation time for the Walden Commune gang, class of '84. Everyone's getting jobs, or getting married, and mercenary madman Uncle Duke plans to turn the beloved house into a resort condo.

That was all there in the play's first brief Broadway incarnation. Now, by plugging into election year electricity and adding new dialogue to keep the few political zingers zingy, Trudeau is hoping to give the show a second life, taking it on a tour of short runs and college campuses.

The adaptors have also taken some liberties with the personalities of some characters, and Doonesbury devotees may not immediately recognize some of the regulars apart from the obvious physical resemblances. Gregg Edelman is particularly fine as proto-Yuppie Mike Doonesbury, who is polishing the third rough draft of his marriage proposal to J.J. (Joanie Caucus' daughter!). And Martin Moran's Zonker is goofily appealing. On the minus side, Paul Kandel is too shrill and hysterical as Duke, and Laura Gardner plays Joanie Caucus closer to Joan Rivers.

Two songs ring particularly false, considering Trudeau's pro-feminist stance. Boopsie's "I Can Have It All" is a Pepsi generation anthem for women whose idea of fulfillment is "marriage, lots of sex and respect, all at the same time." And Honey and Boopsie's duet, "Complicated Man," comes off as a bizarrely reactionary paean to their insensitive men.

The score, by Elizabeth Swados, is bright and breezy, but the slight airs waft out of your head as easily as they float in. Swados' pastiche of pop styles, suggesting everything from country and western to calypso, is just sturdy enough to be used as rhythmic backdrop for Trudeau's words.

And Trudeau shows an obvious flair for lyrics, especially as evidenced by a pair of witty and wicked swipes at the Reagan roster, one in ragtime ("It's the Right Time to Be Rich"), the other in rap (a truncated version of "Rap Master Ronnie," which has just been "spun off" by Trudeau and Swados into a separate off-Broadway revue).

But numbers like those seem out of place in this show. Maybe Trudeau should follow his instincts and sink his theatrical teeth into more of this tougher material, leaving his lovable characters to the funny pages.

DOONESBURY -- At the Warner Theater through Sunday.