Joseph Wambaugh's novels about police life -- "The Choirboys," "The Delta Star," "The Glitter Dome" -- sell like hot Hill Street cakes. My copy of his newest, "The Secrets of Harry Bright," has 149,999 fellows in its first printing alone. Wambaugh's appeal rests in part on an insider's perspective: He used to be a detective with the Los Angeles Police Department. What this means is that legions of reading Americans probably believe the average cop is a buffoon behind a badge.

Such, at least, is the impression left by "The Secrets of Harry Bright," a schizoid novel whose plot veers from farcical episodes involving Keystone Kops with indefatigable libidos to dark interludes of fathers mourning dead sons. The low comedy is generally a thing of the past: Whenever a new character appears, an outlandish anecdote from his or her background can't be far behind.

Consider O.A. Jones, policeman and sole witness to the aftermath of the novel's central mystery. Before learning how he got lost in the desert and stumbled upon a wrecked car containing the burnt and shot-up corpse of a young man, the reader must digest several pages on Jones' incompetence in his previous stint as a patrolman in Palm Springs, Calif.

Jones' greatest lapse was to join in a car chase when he should have been driving a handcuffed suspect to headquarters. He crashed into the chased car, bending his police car in half and killing the suspect. This is all well-told and amusing but has little bearing on the dead boy, Jack Watson, or his father, multimillionaire Victor Watson, who is obsessed with finding out how and why his son died.

Watson's preoccupation impels him to hire a pair of outsiders from the L.A.P.D. to come out to the desert and work on the case. One of them, Sidney Blackpool, has himself recently lost a son in a surfing accident. The idea is that the empathetic Blackpool will pursue the investigation with special fervor. (There is also the carrot of a high-paying job as director of Watson Industries' security force.)

Wambaugh seems to be an energetic researcher. Not content with his ex-cop's savvy, he acknowledges in a preface that he had help from several California police departments in producing the book's "wonderful cop talk." Wonderful it is. Shot suspects have been "ventilated," "You got that right" is the catch phrase of the day; Blackpool's frightened partner confesses, "My neck hair's doing the boogaloo and the freak-a-deek."

The novel closes on an impressively ironic note, for which Wambaugh has been preparing the reader with cunning. Although Blackpool has assembled a persuasive explanation for Jack's death, Victor Watson flatly rejects it -- and Blackpool's candidacy for security director -- because it entails accepting the boy's homosexuality.

All of these facets are so effective that more's the pity Wambaugh stoops to conquer. It is difficult to work up compassion for Watson and Blackpool when one is constantly running across bozos like Prankster Frank, who likes to mace his colleagues' radio mikes ("They didn't know it until they picked it up to talk and their eyes started watering from the gas residue"), or Wingnut Bates, who gets caught in an elevator without his gun, in the company of a prostitute and her armed pimp. "You're under arrest," Wingnut bluffs. "You're dead," says the pimp. "You're not under arrest," Wingnut recants.

This sort of mixing -- the lewd and ludicrous with the passionate and tragic -- requires the utmost skills of someone like Joseph Heller if it is to succeed. These Wambaugh lacks. He can write in all seriousness when he chooses to: his "The Onion Field" is one of the few true-crime stories that can hold its own with Capote's "In Cold Blood." In "The Secrets of Harry Bright," however, he has written not a tragicomedy but a tragedy with a supporting case of giggling schoolboys.