"YOU GAVE AWAY the ending!" a high school classmate of mine -- the same one who brightened physics classes by inquiring whether electrons were alive -- shrieked indignantly at an English teacher who mentioned that Romeo dies at the end of the play. So I will limit myself to saying that the ending of the Loeb's West Side Story is much better than its beginning.

This is just as well, since the beginning is pretty disappointing. The first rumble is confused and unmenacing, the first few songs drag and don't get much of a beat, and Bill Nabel and Jane Eichkern are understandably unable to make their sudden ecstasy of inexplicable love convincing. About the only thing that does work is Peter Agoos's set, which has a fine flavor of New York to it, although even given the city's infinite variety it seems unlikely that Doc's drugstore would charge 30 cents for a Coca-Cola and 29 for a milkshake.

Worst of all, the show seems to be dating badly. Maybe the idea of rewriting Romeo and Juliet as a plea for ethnic tolerance seemed more startling in the '50s than it does now. Maybe putting a gang of Puerto Ricans and a gang of non-Puerto Ricans on the stage and letting them slug it out in a ballet had more impact then. (Maybe Jerome Robbins's choreography was better than this production's, I suppose.) In any event, as a showstopping obscenity, "mother-loving" just doesn't make it any more.

"The tragedy of the show is the convergence of innocent adversity -- Jets and Sharks -- a prelude to trouble," director Guy Rochman explains in a program note for those who might not notice otherwise; but his characters' lives start out seeming a lot more innocent than adverse.

But the production builds steadily, reaching competence towards the end of the first act and threatening to surmount it for the rest of the evening. Nabel and Eichkern both sing well, and though his characterization isn't terribly heroic, her threat to shoot everybody on stage at the end (oh, dear!) is surprisingly solid. Bob Berger's choreography for the dream sequence, and Lindsay Davis's costumes for it -- a set of immaculate white robes for the solemn lookers-on, spotless black for the duellers -- is particularly effective.

Jonathon Scheffer and particularly Jerry Chasen as Maria's luckless fiance do very well by small parts; John Campbell Butman and Maureen Kerrigan as Riff and Anita are fine in large ones. Butman also manages to keep his New York accent comparatively intact and reasonably authentic throughout -- which is rare, although, nobody else quite equals Richard Pimes, who evidently conceives of Doc as a Polish Jew, or possibly anyone else, talk.

Conductor John Posner puts a good deal of life into the later numbers. "Gee, Officer Krupke," which is also cleverly staged, could save the show by itself, even if West Side Story weren't a good enough show, in spite of everything, not to need saving.

"I think it's extraordinary," Leonard Bernstein 39 was overheard remarking at intermission.