Having already served as a hit Broadway comedy and a less successful Richard Lester movie, Terrence McNally's bathhouse farce, ''The Ritz,'' now has a third life, in a manner of speaking, as disco theater. The play opened last night at Xenon. In a season in which several theaters have been transformed into arenas, a show at Xenon reverses the procedure, turning a disco back into a theater. On the still existing proscenium arch, behind the flashing neon, lurks the ghost of the old Henry Miller's Theater.
In dinner theater, one dines and also sees a show. In disco theater, one sees a show and then can stay to dance. While this is a money saver, the new production of ''The Ritz'' is no bargain. Of the three versions of the show I have seen, at the Yale Repertory Theater (under its original title, ''The Tubs''), on Broadway and at Xenon, this is easily the least amusing and the most overbearing.
The story, as you may remember it, deals with a heterosexual garbage man, fleeing from a murderous brother-in-law and taking refuge in a homosexual bathhouse. As a subplot, there is Googie Gomez, a flamboyant singer of no known talent and unlimited chutzpah. She is entertaining at the Ritz while between engagements for ''Fiddler on the Roof'' and ''Oklahoma!'' For her, every role is within her range. The situation, with slammed doors and three people hiding under one bed, is not far from Feydeau. The jokes are frivolous and the atmosphere is intentionally tawdry.
What made the show on Broadway were the performances of Jack Weston as the garbage man and, especially, Rita Moreno as Googie. While Taylor Reed fills the requirements of the former role - he is chubby and easily agitated - he lacks his predecessor's bedazzlement. Googie survives in our memory of Miss Moreno. In the current production, the role is undertaken by Holly Woodlawn, a transvestite actor of Andy Warhol movie fame. He is not bad, but he is not Googie. As an actor pretending to be a woman who is mistaken for a man, he is far less funny, for example, than Julie Andrews was in almost the reverse situation.
A few of the actors keep the comedy from flagging, including Michael Greer as the camp queen of the frolic and Casey Donovan as the falsetto-voiced detective who tries to unravel the mistaken identities. The problem is not so much in any single performance as in the insistence of Michael Baver's production, which is about as subtle as a a wet towel.
''The Ritz'' should have been given a longer rest. As for the talented author, he has a ferocious sense of humor when dealing with actors, producers and playwrights, as he also demonstrated in his theatrical comedies, ''Bad Habits'' and ''It's Only a Play.'' Mr. McNally may yet write a ''Once in a Lifetime'' for our time.