If you accept the basic premise that a comedy about homosexual sadomasochists can be an enjoyable evening's fare, there is considerable promise in Doric Wilson's "The West Street Gang," which will be playing at the New Back Alley, Thursdays through Sundays, throudh March 30.

Most of the promise, however, is in the first act, which has many moments of wild if somewhat specialized humor. The second act turns into an extended Anita Bryant joke -- an art form that, like its subject, passed its peak some time ago.

At first glance, "The West Street Gang" has some resemblance to an earlier production at this theater which was a resounding success: "P.S., Your Cat Is Dead." This was also a comedy with sadomasochistic, homosexual overtones, but in its kinky way it came to terms with some basic problems of human relations that are equally important to straights and gays -- problems of openness and vulnerability versus dominance and manipulation; problems of the individual looking for identity and security in a hostile world.

If any theme manages to emerge from "The West Street Gang," it is that of homosexuals' failure, as a group, to establish a positive place for themselves in society. The theme seems out of date today, when significant progress is being made on that front, and it is treated with so little coherence that the show finally dissolves into a series of jokes -- good, bad and indifferent, including some that are not very good but are rescued by good acting.

With all its problems, this play is the kind of show that the New Back Alley company does well -- contemporary, unpretentious and offbeat, with the kind of intimacy that is essential in a house where 100 customers are a standing-room crowd. All the roles (as one of the characters remarks) are caricatures, and the prevailing style of acting is appropriately outrageous.

Best and most outrageous of all is Raymond Green as a transvestite, Shanghai Lil. Also noteworthy, in a cameo sort of way, are John Voorhees as a world-weary old barfly, Neal Flieger as a "maleactormodel-dancersinger," Tom Loftis as a midnight cowboy and Jackie LaBarro as the female half of a police team named "Bonnie and Clyde."