LOS ANGELES (AP) _ It may be the most unsettling movie scene this year, and it doesn't involve Hannibal ''The Cannibal'' Lecter, some zombies under the stairs or the murderous doll from ''Child's Play III.''

In fact, no blood spills in this disturbing episode from the otherwise bloody thriller ''Cape Fear.'' The 10-minute scene is all about menace and innocence, and it is galvanized by the performances of Robert De Niro and Juliette Lewis.

Miss Lewis plays the rebellious 15-year-old daughter of a lawyer who withheld evidence in his defense of rapist Max Cady (De Niro). Cady's psychopathic wrath has flamed for 14 years in jail. Once freed, he sets out for revenge, targeting lawyer Sam Bowden (Nick Nolte), his wife, Leigh (Jessica Lange), and their daughter, Danielle (Miss Lewis).

In the film's most disturbing moment, Cady poses as a sympathetic drama teacher to lure Danielle to an abandoned high-school theater. The audience knows the danger, but Danielle wanders unafraid into the auditorium, actually curious to meet this substitute instructor who was so considerate on the telephone the night before.

He smokes marijuana, offers her a puff. He makes sexual advances, she doesn't retreat. She figures out that he's not a teacher but instead is stalking her family. She doesn't run. It's spooky.

Miss Lewis says it's the best work she's done in what is already a varied career.

''After the scene, I told (director) Marty (Scorsese) and Bob, 'God 3/8 That was so fun 3/8''' she said in an interview. ''That was the only scene I've ever done in six years where I've felt that type of satisfaction and that type of excitement and fun.

''I tried to fill Danny out as best I could, make her as real to a young girl as I could. She's so innocent. That's what's scary. Some people ask me, 'What made her attracted to evil?' And there was nothing like that at all.

''She was oblivious. This guy was letting her speak, looking at her as an equal, and she was drawn to that. It's total innocence. And that's what scared people: evil and innocence. People hurting animals is more frightening than adults being hurt.''

Miss Lewis, who's 18 but appears much younger both in person and on screen, is hardly as innocent as the ''Cape Fear'' character she plays.

She left high school three weeks into her freshman year to establish her career and went to court at age 14 to have herself declared an adult. She lives with her 27-year-old boyfriend of two years, actor Brad Pitt (''Thelma and Louise''). And while her locally bred vocabulary is cluttered with endless ''totallys,'' ''likes'' and ''you knows,'' she seems fairly savvy, grown up fast.

The daughter of actor Geoffrey Lewis (''Double Impact,'' ''The Great Waldo Pepper''), her credits include the television projects ''Too Young to Die?,'' ''A Family for Joe,'' ''I Married Dora'' and ''The Wonder Years.'' On film, she has appeared in ''National Lampoon's Christmas Vacation'' and ''Crooked Hearts,'' in which she plays the narcoleptic daughter of a troubled family. She will star in next year's ''That Night,'' adapted from the Alice McDermott novel.

''She's a major talent,'' said Dale Pollock, the producer of ''Crooked Hearts.''

''She doesn't even realize how good she is. She's the most talented newcomer around. And an incredibly natural actor.''

It's a profession to which Miss Lewis has aspired since she was 6.

''I went to about three weeks of high school,'' she said. ''I moved out of the (San Fernando) Valley to Hollywood. I just wanted to move - the Valley is a very sort of teen-age land, a very weird scene. I wanted to focus on my profession. So I went to a tutor and studied for the proficiency test,'' an equivalent of a high school diploma.

She passed at age 15.

''It doesn't mean I'm going to stop educating myself. It just means I'm not going to do it in the structured, public school, weird way of schooling. I'm just trying to establish my career. .. . It was to start life now rather then when I'm 20. And I felt sort of, like, ready for that.

''I don't know any other kids that have done it like me. I always have this problem that I might sound arrogant. But it's just confident.''

She says Scorsese allowed her to create the character. She was 17 when it was filmed.

''Danny was written as your standard, generic teen-ager. The script was the front. And I just filled in all the little stuff in a young girl's mind. I was allowed to do that. Most directors who are not brilliant like Marty would always stifle me. They would tell me not to do this, not to do that.

''They're used to mediocre stuff and they don't want anything too real. It's scares them or something.''