Appropriately enough, the strongest moment in "Side Man," which opened last night at the Kennedy Center, is a purely musical one. The side man of the title, Gene (Michael O'Keefe), and two of his musician buddies are listening to an amateur tape recording that captured the legendary last trumpet solo of jazz great Clifford Brown a couple of hours before he died in a car crash.

The playing is extraordinary--dizzying, almost skittish, but with the punch of a boxer--and, as the sound swells from the tiny tape recorder to take over the Eisenhower Theater's sound system, the three men are transported to a different and finer world.

In spite of this scene and its setting in the world of on-the-edge jazzmen, Warren Leight's play isn't really about music. It's another father-son play in which the son looks back and tries to understand Dad and forgive him for being such a jerk.

Gene's life--told in flashbacks and imagined scenes by his son Clifford (Andrew McCarthy), named after his father's musical hero--is a small one. And it only gets smaller as time passes and the big bands with whom Gene works fall by the wayside, choking on the cultural dust kicked up by that frenzied new arrival rock-and-roll.

Most of the drama centers on Gene's disastrous marriage to the unstable, finally alcoholic Terry (Angelica Torn). Theirs is a classic bad marriage. She's high-strung and likes to plan; he's pathologically easygoing, dealing with problems by denying they're there. She looks like the villainess and he looks like the long-suffering husband, until you notice how his avoidance is a form of aggression against this unwanted wife and son. Toward the end, when Clifford tries to talk to him about Terry's decades of alcoholism, Gene merely murmurs, "I don't think it was that bad." When his family tries to grapple with him, he turns into a cloud of innocent incomprehension and leaves them clawing at the air.

Gene is potentially a great character. Like those other monster-fathers of the American stage--James Tyrone in "Long Day's Journey Into Night" and Willy Loman in "Death of a Salesman"--his weapons are elusiveness and denial. Unlike them, his style is not pugnacious. A true hipster, Gene anticipates and acts out the coming Zeitgeist of the '60s: He has dropped out.

Unfortunately, O'Keefe's Gene is an oddly colorless performance. He doesn't come across as a drifting, reality-dodging dreamer; he's just bland. His amiability has no malevolent undertone. There doesn't seem to be enough there for his wife to hate and his son to feel guilty about.

"Side Man" isn't constructed dramatically--that is to say, it doesn't build so that as the evening goes on our understanding of the situation becomes deeper and more complex. It's basically a string of scenes, although some of them, such as a nightmare supper at home for young Cliff, are real successes. Some of them are merely pleasant.

Outside of the marriage, the characters are conceived in cliches--the tough girl with a good heart, the out-of-it hipster who is wiser than anyone else, the kvetching fussbudget.

Andrew McCarthy can hold a stage and center a play, even though his comic takes tend to be overdone. (Director Michael Mayer has allowed a lot of near-mugging from the cast.) As bitter, volatile Terry, Torn is by turns shrewishly unsympathetic and surprisingly touching.

Finally, Clifford, who has seen himself as his parents' caretaker, gains his psychological freedom and leaves New York for the West Coast. In keeping with the play's lack of drama, the audience isn't told how or why this happens--it seems to occur because it's time for the play to end.

The portrait-of-a-horrible-marriage is the most compelling element of "Side Man." The scenes with the other musicians--playboy Al (Joseph Lyle Taylor), fussy Ziggy (Michael Mastro) and hip Jonesy (Kevin Geer)--are mostly an excuse to tell stories about jazz. Some of these stories are pretty fabulous, but they play like interludes from the real action, that dreadful marriage.

Side Man by Warren Leight. Directed by Michael Mayer; set, Neil Patel; lights, Kenneth Posner; costumes, Tom Broecker; sound, Raymond D. Schilke. With Marissa Matrone. At the Kennedy Center through Nov. 28. Call 202-467-4600.

CAPTION: Michael O'Keefe and Andrew McCarthy as a father and son at odds.

CAPTION: Angelica Torn, Andrew McCarthy and Kevin Geer in "Side Man."