Frank London makes his living adhering to the adage "what's old is new again."  But he believes that what's old has to be mastered, understood, and respected before what's new takes shape.
   "There are tow ways you can think of being a revolutionary," London said during a recent interview in the vacant lobby of the Prince Music Theater.  "One is to reject.The other is to take, but transform.  That's the path I've always worked, whether it's in jazz, whether it's in anything."
   Current;y, his path is the musical drama "Green Violin," which has its world premier at the Prince tomorrow and runs through May 18.
   London wrte the klezer-based score for a tale that explores the relationship between Solomon Mikhoels (played by Raul Esparza), the lead actor inthe Mosow State Yiddish Theater (GOSET), and Russian painter Marc Chagall (Hal Robinason), who created the thater's sets, costumes and makeup.  Chagall reportedly painted the theater's walls and ceiling-- including a mural, "Introduction to Yiddish Theater"-- in 40 days.
   London is a trumpeter and composer who has made his name, for the most part, with bands such as the Klezmatics and the Hasidic New Wave that play contemporary klezmer music, fusing jazz and avant garde styles with traditional Jewish instrumental music.
   "The word 'radical' actually means, linguistically, 'roots' " London said.  "So you're being radical b going to the roots of something."
   And for London, 44, of Brooklyn, going to the roots is part of the fun.  "I love that, the looking at something, studying it, picking it apart, knowing how to be yourself at the same time."
   London has been called "one of the most influential musicians in contemporary klezmer," but he didn't startout being an expert on klezmer music.  He was Jewish, not a particualrly religious Jew.  His first gigs were with Latin and salsa bands, where horns are prominant.
   He developed a taste fr jazz, especially the more edgy type, then was introduced to klezmer music by a professot while attending the New England Conservatory in Boston.
   London spent time in Philadelphia during the late '80s.  He recalled playing wit the Wild Magnolia Brass Band during Mardi Gra, and jam sessions at Ortlieb's, where he heard tenor saxman Bootsie Barnes.  And he recalled playing with Lester Bowie's Brass Fantasy a the Painted Bride.
   "What [Bowie] and those people did when they were really revolutionizing jazz, they went back to early jazz as an inspiration to how they made a modern music," London said.  "That's the same impulse at work here."
   "Green Violin" is set in the Moscow State Yiddish Theater, founded in 1919.  Legendary Jewish actors, writers and artists, such as Chagall, Peretz Markish, Isaac Babel and Mikhoels worked there.  The theater, which did shows such as a Yiddish "King Lear" and toured in the 1920s and '30s, maintained Yiddish culture until Joseph Stalin, fearful that theater audiences were being stirred up against his regime, killed it in1949.
   For London, who has been doning klezmer music for more than 20 years, mingling the old with he new within the constraints of storytelling was gratifying.  "It's fun to give yourself rules and structure and then use that to experiment with," he said.
   "That's true to what Chagall did, and what a lot of cubists did.  They were painting in a certain way-- realism they had broken up in a structural way.  They took the canvas and fractured t, but then they painted sort of realist.  That's what made it modern."
  London has written for film and theater musicals before, but "Green Violin" was still a little different.
   "What's fun about this peiece for me as a composer is we're doing a musical about theater.  And within our play are excerpts from three other plays," London said.  "So I made this musical choice to make each of the three sub-plays have a different musical attitude."
   One sub-play has a gritty, "Tom Waits, punk-roots, cabaret" feel.  In the second, "I tried to write a miniature opera."  In the third, a Yiddish version of "King Lear," "we went just for a sort of modern, classical underscoring."
   London, who got the script only last summer, collaborated with wirter ELise Thoron and director/co-writer Rebecca Bayla Taichman to assure the songs "serve the bigger picture."
   The Prince production will ave a five-piece band, led by paianist and music director Steve Bishop, including a percussionist, cellist, woodwind player and violinist Max Zorn.  London won't perform.
   With his klezmer work, London's a big fish in a small pond, but having a niche has its advantages.
   "In this world I have a bigger reputation and can command a bigger salary," he said.  "But if I go out there with a jazzsextet, [there's] me and a million other guys.  I'm just one of them.  I'm not going to get a call from the North Sea Jazz Festival doing my Artt Blakeish band, but I will go to North Sea when I'm doing something based on this world, which is unique."