The influences on Burr Steers's plucky portrait of adolescent dysfunction range from J.D. Salinger's The Catcher in the Rye to Larry Clark's Kids. Despite the familiar material, Steers delivers something fresh, provocative, and unadulterated. Kieran Culkin's Igby is a baby-faced imp who has mixed feelings about his dying mother (Susan Sarandon) and unmitigated contempt for his dutiful brother Oliver (Ryan Phillippe). Kicked out of one boarding school after another, Igby decides to drop out by squatting in the Manhattan loft of the mistress (Amanda Peet) of his sardonic uncle (Jeff Goldblum). Matters deteriorate when Igby beds Rachel while the hated Oliver chases after Sookie (Claire Danes), the girl Igby really loves. Much of the film, which Steers wrote as well as directed, hangs on Culkin's performance, and though the young actor expresess angst with flair, his inconsistent level of maturity -- sometimes he seems 12, other times 30 -- lacks credibility. It's a minor flaw in an otherwise masterful filmmaking debut by Steers, with outstanding supporting performances by Goldblum and Peet. (97 minutes) At the Avon.