Says Brussell, a kind of klezmer visionary, "There's something powerful and ancient about this music, something that cuts to the core of the Jewish experience."

Beginning at 7:30 p.m. Oct. 15 at Congregation Emanu-El in San Francisco, the festival is co-sponsored by the synagogue and the Jewish Bulletin of Northern California. On the program are cantor Roslyn Barak, who will perform songs from the Yiddish theater, the Norbert Stachel Kleztet and Klezmania!, both of which will play 30- and 50-minute sets of mostly traditional klezmer tunes with contemporary twists.

Klezmania! will perform "Yiddishe Meydele," "Yoshke, Yoshke," and "Maz'l" — all traditional songs from the klezmer repertoire — but the tango rhythm of "Yiddishe Meydele" lends itself to jazz-style improvisation, Brussell says.

Klezmer's improvisational style hit home for Brussell on a visit to Israel in January 1994. Invited to jam with clarinetist Mousa Berlin's band during a klezmer festival at a settlement just outside Tel Aviv, Brussell was struck by how klezmer was so well-integrated with the community's religious and political identity.

"They would play a song, then say a prayer," he recalls. "Or they would play a song, then comment on the state of affairs in Israel. I saw that klezmer was woven into the whole experience of this particular Ashkenazic culture."

Brussell promises he won't indulge in any political rhetoric at the Klez Fest. The evening will be devoted to music, but when Brussell and Stachel speak about klezmer, certain political overtones emerge.

They see klezmer becoming a virtuosic form like jazz, which has moved from its origins in primitive folk rhythms to a classical complexity. Both Brussell and Stachel distance themselves from klezmer purists, who want to exclude certain kinds of instruments and influences from klezmer.

On Sunday, Stachel's band will include a tuba taking on the role usually filled by a bass violin; Klezmania! incorporates an oud, a fretless Persian string instrument that Brussell describes as looking like a "fat, squat guitar with a short neck."

"Fretted instruments can't get that kind of Middle Eastern glissando sound the oud can," he says.

Klezmania's use of a soprano saxophone (rather than the traditional clarinet) has also drawn the band some criticism, which Brussell acknowledges but shrugs off.

"I'm a fusion klezmer artist," he says. "If people want to hear pure klezmer from us, they'll be disappointed. It makes me crazy to play something the same way over and over again."

"Any art form needs to evolve and grow and stay open to new influences. I came home from Israel with 40 albums of Israeli music, both Jewish and Muslim. A lot of the Arabic music is incredible."

Stachel concurs. "I enjoy and respect all kinds of music around me," he says. He likens klezmer to what he called "the great African American musical blending," stretching from ancient African rhythms to contemporary hip-hop and rap.

In fact klezmer, he says, is one of the world's must integrated musical forms. From the word klezeimer, which means "musical instruments" in Yiddish, klezmer is a street music derived from various folk sources: Eastern European melodies, Yiddish stylistic idioms, and Slavic and Turkish influences from the Ottoman Empire era.

Klezmer also contains classical harmonies and, especially, elements of rabbinical music, giving the music its Jewish flavor, a unique combination of minor-key melancholy and joy. Despite Brussell's and Stachel's embrace of other influences, Stachel says klezmer should always keep its roots in Jewish musical styles — but should be free to blend with the culture in which it is played.

"To manipulate things unnaturally is anti-musical," he says, "but if a natural cross-relationship develops between musical forms, it should be allowed to happen."