''I wanna introduce my homegirl, Miri Ben-Ari, the hip-hop violinist!'' cried Kanye West midway through a set in Manhattan this spring. ''She's gonna help me out with this one.'' Ben-Ari slinked on stage, frizzy-haired and lithe and small, with her pale midriff exposed, and tore the opening hacksaw notes of West's ''The New Workout Plan'' out of her fiddle. Then, after the song, West went backstage to change his polo, and something amazing happened: Ben-Ari, on her own, got the hip-hop crowd hooting with just a violin, whizzing through solo versions of famous rap songs like Jay-Z's ''Dirt Off Your Shoulder'' and ending to giant applause. She pretty much stole the show. Who is she? The 26-year-old, classically trained Israeli violinist who says she's ''real gangsta on the instrument'' worked on 90 percent of West's hit album The College Dropout and pops up for a cameo in his crazy new ''Workout Plan'' video. Plus, she bowed (and scowled) prominently in Twista's ''Overnight Celebrity'' clip this summer. And early next year with help from a bevy of rap royalty she'll release her own solo CD, Miri Ben-Ari: The Hip-Hop Violinist. The first single, ''Sunshine to the Rain,'' featuring Scarface and Anthony Hamilton, hits later this fall. As Ben-Ari herself notes, ''What other instrumentalists except for Santana and Kenny G have major careers? I don't know anybody. A third person like that? Whoa.'' Word.