Remember "The Ladies Who Lunch," the snarling appreciation of the empty lives of wealthy middle-aged matrons that was a high point of the Stephen Sondheim/George Furth musical "Company"? Imagine how that bitter number might have sounded had it been given not to Elaine Stritch, but to Rebecca of Sunnybrook Farm instead. If you can, you have a notion of the general impression imparted by Sondheim and Furth's most recent collaboration, "Merrily We Roll Along," which opened Monday at the Alvin Theatre.

This is an eminently jarring musical. The fault doesn't lie entirely with Furth's superficial script, although it certainly spins a grating tale of seeping disenchantment and idealism turned rancid. Nor does the fault lie entirely with the youthful performers, who are pretty much at the beginning of their careers in the musical theater and tend to be more energetic than skilled. No, the real problem is that this decidedly fresh-faced cast is being asked to depict the sorry compromises, the world-weariness and the professional bitchiness that presumably come much later in a lifetime.

"Merrily We Roll Along" is adapted from the 1934 Kaufman and Hart drama of the same name, which traced the moral disintegration of a big-time Broadway playwright and some of his close friends. Kaufman and Hart told the familiar tale in reverse order, however. They began by showing us a rotten individual at the pinnacle of success. The succeeding scenes worked backward in time -- through the failed marriages, the tawdry affairs, the petty betrayals -- and ended up with the playwright as a starry-eyed high school graduate, urging his classmates in his valedictory speech "to thine own self be true."

The musical retains the same scheme with a few alterations. The playwright, Franklin Shepard, is now a composer, half of a successful Broadway songwriting team. When we first meet him, he has just overproduced a worthless motion picture in Hollywood and his integrity is shot. The ensuing scenes retrace his footsteps back to Lake Forest Academy in Illinois in the mid-1950s. There are stops at the Polo Lounge, a TV studio in Radio City (where Franklin breaks up with his partner), Broadway (for the first big hit), Greenwich Village (for the early struggles), and finally a rooftop on 110th Street, where our hero gazes at Sputnik skimming overhead and finds himself filled with silvery wonder for a world in which anything is possible. Dogging him along the way are a sharp-witted woman novelist who loves him from the sidelines while he jumps from one bedmate to the next, and his good-natured lyricist, who wants only to write respectable shows, not smash properties.

Obviously, such a saga is not wildly cheerful, emphasizing as it does the fact that time erodes all good aspirations and that ideals can't hold a candle to the trinkets of fame. Still, what is utterly disheartening and fatal about the musical is the decision to have it acted by youngsters, whose primary asset is their untarnished innocence. Most of these performers are in way over their depth -- or over their years -- playing the cynical, the craven, the avaricious and the mean-spirited -- in short, a whole shooting gallery of show business types who have struck a bargain, and not a pleasant one, with life. Having them toss back the booze, swap tired party quips, stab and seduce one another is disquieting, when it is not ridiculous. "I don't change," snaps an actress who is playing one of the monied sharks in Broadway's troubled waters, although she looks suspiciously like a bobby-soxer. "I just change the people around me." One wants to pat the sweet girl on the head and counsel her to grow up. Only toward the end of the evening, when the musical has edged closer to high school, do the performers' age and experience begin to match up. By then, it's too late.

Sondheim has written some of his most insinuating melodies to accompany the retreat of time. "Good Thing Going" and "Not a Day Goes By" are both plaintive acknowledgments of the fragility of love and partnership. "Now You Know" has an infectious sock-hop swing, and the title tune, especially as arranged by Jonathan Tunick, pulsates with the promise of exciting things to come. And yet I suspect that this score, with its acute awareness of human heartbreak, would really prove more moving out of the show's context.

Director Harold Prince, whose collaboration with Sondheim has resulted in some of our more distinctive musicals ("Sweeney Todd," "A Little Night Music," "Follies") has been unable to galvanize this one. It unfolds on high-tech sets by Eugene Lee that are so much boring hardware. Larry Fuller's choreography is minimal, and Judith Dolan's costumes are merely dressed up T-shirts. Each one carries an identifying logo -- best friend, novelist, producer, maid -- which is almost an admission that in the sea of unlined faces it would otherwise be hard to differentiate one hard-bitten character from the next.

Jim Walton, as the egocentric composer, has a blond all-American presence, more appropriate for breakfast cereal commercials. Ann Morrison, as the novelist and sidekick, a character Kaufman and Hart modeled after Dorothy Parker, appears to be halfway to a Tallulah Bankhead imitation. As the decent lyricist, Lonny Price projects a certain frizzy-haired charm but he is not up to the intricate patter of "Franklin Shepard Inc.," Sondheim's musical chronicle of the daily harassments of an artist once he sells out and becomes a corporation.

But the cast members really aren't all to blame. In "Merrily We Roll Along" they've been saddled with a heavy load of corruption. It's a little like expecting Juliet to stand in for Lady Macbeth.

MERRILY WE ROLL ALONG. Music and lyrics by Stephen Sondheim; book by George Furth; directed by Harold Prince; choreography, Larry Fuller; sets, Eugene Lee; costumes, Judith Dolan; lighting, David Hersey. With Jim Walton, Ann Morrison, Lonny Price, Sally Klein, Jason Alexander, Terry Finn. At the Alvin Theatre.