West Side Story, like all good theater, is full of illusions.

But some illusions, even in the best of theater, just don't work. The Port City Playhouse production of West Side Story, now ending a four-week run in Alexandria, is a case in point. The producers seemed to think it is possible to fit a cast of 50 onto the stage of a high school auditorium and successfully execute the full-blown production numbers that have made Leonard Bernstein's 25-year-old classic so memorable to so many audiences.

Well, it seems, they were wrong.

It's not that the dancing isn't exciting; it's just that so many of the heart-stopping thrills come from watching dancers miss each other and the scenery by fractions of degrees.

The limitations of the stage are unfortunate, for the young dancers have all the exuberance of the teen-agers they portray, and Playhouse officials had hoped to make the choreography the strength of this production.

Playhouse spokesman Tom Miller said the theater group ran a special dance workshop for the show starting last October and chose most of their cast from among 75 workshop graduates.

But the ambitious production does have its strong points: Powerful singing by the male lead and strong performances from the three major supporting characters.

Nearly everyone is familiar with the story line: the old Romeo and Juliet tale, translated to the streets and street gangs of New York.

In the Port City production, the two leads, Maria (Athena Bouras) and Tony (Robert Kramer), seem to have been chosen for their singing talents alone, while the three supporting characters, Anita (Gilly Conklin), Riff (Tim Lynch) and Bernardo (Charles Nixon), show a certain acting ability. Conklin, a last-minute substitute in the show, is the strongest of the three, playing the street-wise Puerto Rican girlfriend of a gang leader with just the right blend of toughness and compassion. Lynch and Nixon handle the gang leaders' roles with adequate believability; besides, Lynch can sing, and they both can dance.

Acting is not the strongest suit of the leading pair.

Bouras, a beautiful soprano, plays an incredibly naive Maria. Kramer portrays Tony as the most innocent of young men, walking into the deadly romance with Maria with all the cunning and intelligence of a patch of moss.

But never mind: The man can sing (if sometimes a little faster than the orchestra) and he looks awfully cute in his underwear in the bedroom scene.

Which brings us to the subject of ribaldry. The playhouse version of West Side Story has more of this than the original version and although the bedroom and rape scenes are quite tame, there is enough genital rubbing and "mother f-----g" in it to offend many people.

But the foul language comes off as the natural street talk of the two rival gangs, especially as the play builds to the finale of the all-out rumble. And one of the high points of the Port City production comes when the whole, massive cast sings about the coming rumble in a wonderful, show-shopping "Tonight."

As always, though, the real heartbreaker is when the dying Tony joins with Maria in a reprise of "There's a Place for Us," in a lovely duet.

"West Side Story" is so much nicer than most theater that nearly any production is worth watching, and Playhouse does credit to Leonard Bernstein's music and Stephen Sondheim's lyrics. What the Playhouse dancers lack in control, they make up for in exuberance and bravery on that tiny stage.

Port City Playhouse's "West Side Story" runs Aug. 13 and 14 at 8 p.m. in the Mini Howard Auditorium, 3801 West Braddock Rd., Alexandria. Tickets are $5 for adults; $3 for students and senior citizens. Call 549-8592 for reservations and information.