Forget for a moment that the year is 2004 and you're actually on Murray Street. Walk in, take a seat, and imagine yourself in an Algonquin-like nightspot in post-World War II Manhattan. You are surrounded by a few dozen theatrical luminaries like yourself, urbane, witty, musically inventive, and ready-yes-for Broadway!

This is the fantasy of "Spontaneous (West) Broadway," an improvised musical production, in two acts, coming to Tribeca's Black Watch Stages, a film production studio turned 50-seat theater for performances that run from June 4 to June 20.

"Spontaneous (West) Broadway," is the work of Freestyle Rep, a long-standing seven-member troupe that is coming to Tribeca after the Trilogy Theater, it's venue on West 44th Street, lost its lease. "Spontaneous (West) Broadway," is one of six shows in the group's repertoire.

In the first act, the performers take their cues from the audience, who suggest song titles and other ideas for a musical production.

"We get wonderful inspirations from the audience," said Michael Durken, a member of the company. "It's always nice if it is not intentionally funny or too original."

A half-dozen songs are created and during intermission the audience decides which will become the inspiration for a full-blown musical, with background, costume, and props-some of which, of course, are imaginary.

No two performances are alike, says Durken, but the audience is treated to a true theatrical experience all the same.

"What an actor does on stage is try to make the moment real," he said. "That's what we do, only we do it spontaneously."

"Spontaneous (West) Broadway) is performed Fridays and Saturdays at 8 p.m. and Sundays at 7 p.m. at Black Watch Stages, 49 Murray St. Tickets are $12. Call 212-868-4444 or go to www.smarttix.com.