SHE PUT THE BLUE IN NYPD BLUE'S FIRST SEASON—AND THOSE steamy scenes with David Caruso paid off in a movie career. Amy Brenneman follows up her lengthy kiss with Paul Reiser in Bye Bye, Love by costarring with Al Pacino and Robert De Niro in next fall's Heat. "She's got this marvelous natural beauty," says the thriller's director, Michael Mann, though Brenneman, 30, claims the camera exaggerates her appeal: "For some reason, I just photograph very smoldery." The Connecticut-bred daughter of Russell, an attorney, and Frederica, a superior court judge, Brenneman wound up at Harvard but after graduation came back to acting, which she started at 11, "when I was all legs and frizzy hair." Now engaged to Casper director Brad Silberling, she tries to keep her memorable head on straight. "Like anybody, I can obsess about beauty on a b.s. level," she says. "The trouble with that level is that if you're not careful, you can live there."