Among the Los Angeles patrolmen characterized - or, to be precise, caricatured - in "The Choirboys," now at area theaters, the term "choir practice" is a euphemism for an all-night drunken toot in MacArthur Park. At some stage the original author, Joseph Wambaugh, and the director, Robert Aldrich, must have envisioned a profane popular comedy patterned after "M*A*S*H," with the choir practicesserving the same purpose for overworked, pressured and sometimes brutalized urban cops that the binges and practical jokes served for the battle surgeons in Robert Altman's film.

"The Choirboys" belongs to the tradition of service comedies, but I doubt if anyone will hail it for doing a service for either cops or movie auidences. If the filmmakers had ironic or satirical intentions, the finished film totally obscures them. There's no contrast between cops at work and play. The whole movie suggests a dirtyminded "McHale's Navy," with scenes pivoting on gross set jokes alternating with scenes pivoting on grosser sick jokes.

Some of the jokes are so raucously or goofily low-minded that you may laugh out of a kind of shocked weakness. At a certain level there is something funny about the idea of a drunken slob creeping under a glass-topped coffee table to get a peek up a women's skirt or the idea of a jumper being provoked to her doom by a cop who tries to use reverse psychology and dares her to "go ahead and jump."

However, once commiting your entertainment in this direction, it may be impossible to change. Towards the end "Choirboys" attempts to get serious about the sordidness that it has been wallowing in for gratuitious, episodic laughs, and this switch seems both deceitful and laughable. It's much too late to take a different tack, and at the fadeout the mood returns to cackling facetiousness. The promotion for this movie should probably be built mately, neither the filmmakers nor the characters feel any credible pain. They're just rowdy fraternity boys in blue.

Wambaugh, who did the original adaptation of his own best-selling novel, has been busy disowning the film. He succeeded in having his name removed from the screenwriting credits and placed an ad in movie trade papers complaining that Aldrich had done him wrong. It's difficult to see how. The comic vulgarity originated in the novel, and surely no one could imagine the director of "The Dirty Dozen," "The Longest Yard," "Hustle" "The Killing of Sister George" and "Whatever Happened to Baby Jane?" suddenly developing a delicate touch.

It's more likely that Wambaugh came to the realization that visualizing this colection of tales told out of school could be more embarrassing and misleading than simply publishing them. "The Choirboys" is a vaudeville of precinct scandals and follies that may not mean the same thing to cops that they mean to civilians. Although he supplied the pretext and context, Wambaugh may not care to associate himself with the misconceptions about police work and psychology that could result from the film version.

"The Choirboys" takes a fairly obnoxious place among a burgeoning genre of Hollywood films determined to revel in raunchiness. "Slap Shot" set, the pace earlier this year. Now we have "Looking for Mr. Goodbar," "Saturday Night Fever," "The Gauntlet" "The Choirboy" and even "The World's Greatest Lover" straining to keep up, The spectre of television must be partly responsible: To a certain extent these movies recommed themselves because they'll need to be expurgated for telecasting.

Charles Durning has the most prominent role in a large, able but largely wasted cast as the hard-bitten patrolman "Spermwhale" Whalen, suggesting a cross between Spencer Tracy and Los Costello. Not too surprisingly, Burt Young creates the most human and appealing impression as a motley-looking but gentle natured vice cop. Tim McIntire also gets something distinctive into the boobytrapped assignment of the resident redneck bigot. Robert Webber cops the booby prize for his teethgrinding closeups as, naturally a mealy-mouthed brasshat.