No performer who relishes dancing on the edge would turn down the opportunity to play a drug addict, and so you can understand why Leonardo DiCaprio, the audacious young actor from ''This Boy's Life'' and ''What's Eating Gilbert Grape,'' would have wanted to star in The Basketball Diaries, an adaptation of Jim Carroll's 1963 underground memoir, in which the New York poet, author, and musician chronicled his teenage descent into heroin addiction. Late in the film, when Carroll has fallen into the gutter, DiCaprio has a scene that can stand as one of the supreme harrowing moments in junkie- movie history: He bangs on the door of his mother's apartment, begging for cash (to buy more drugs, of course), and when Mom (Lorraine Bracco) refuses to give it to him, he keeps repeating his anguished cry for ''money,'' until the word itself devolves into a wail from the abyss.
In that one scene, DiCaprio is brilliant. Yet I had major problems with the rest of his performance. It's hardly the actor's fault that at 17 he looks 12. But in playing Carroll, the working-class Catholic bohemian, DiCaprio never seems like a true street kid. He's too sleek and white-bread and suburban, and the scenes in which he makes mischief with his jerky pals (including Mark Wahlberg, ne Marky Mark, very convincing as an insensitive mush-mouthed lout) are like something out of a bad juvenile-delinquent flick. The decision to transpose Carroll's story from the '60s to the present day gives ''The Basketball Diaries'' a hazy, dissatisfying tone. The film can't make up its mind whether to celebrate the rowdy nihilism of Carroll and his cronies or to present it in stark, objective terms, and so we never quite get a fix on who Carroll is, or why we should care about this cocky Cheshire cat of a kid who writes agonizingly banal high school poetry (which the movie seems to think is art). Still, if ''The Basketball Diaries'' is a mess, it's an energetic, watchable mess. And for those few soul-freezing moments, you get a glimpse of the great actor Leonardo DiCaprio is going to be.