Isabelle Huppert, an actress for the ages, gives one of her supreme performances as a sexually perverse pianist in Michael Haneke's "The Piano Teacher," a film that coolly juxtaposes the sublime and loathsome, the tender and terrible.

Based on Elfriede Jelinek's novel of a sadomasochistic relationship played out against the spartan, highly competitive world of classical music, this is a movie so fiercely candid that some audiences may find it hard to take. That was almost how I felt when I first saw "The Piano Teacher" at the Cannes Film Festival, where it won three major awards - the Grand Prize and Best Actress and Best Actor awards for Huppert and her 27-year-old co-star, Benoit Magimel - despite loud boos at the audience screening.

"The Piano Teacher" may not have deserved all three of those top awards, but it's still a striking, brilliant film with extraordinary performances - and Huppert's acting is heartrending. She plays Erika Kohut, a consummate but outwardly emotionless pianist and master-class teacher. She excels at interpreting Schubert but lives a lonely and painful life with her tyrannical mother (Annie Girardot) and finds sexual solace in pornography and acts of self-mutilation. Magimel plays Walter Klemmer, her charming, gifted student, a golden child of affluence and culture who idolizes Erika for her mastery, pursues her - and then, with increasing shock and revulsion, is pulled into her dark and emotionally destructive private world.

The couple, who join for some of the most unbearable and frightening love scenes ever (brutal trysts where most of the action is masked), fall into a hell of irresolvable differences. For the repressed martinet Erika, sex is evil and hurtful, just as her censorious mother views it. (The mother and daughter sleep in near-incestuous proximity in twin beds shoved so closely together they resemble one - and the mother, agonizingly well-played by one-time screen siren Girardot, nurtures her daughter's art and damns her sexuality. For Walter, on the other hand, sex is natural and easy, an open flood of unashamed sexuality. These two views cannot coexist, and when Erika attempts to tyrannize Walter - to dominate his sexuality just as she dictates his piano playing - the pair are headed for disaster. He becomes as cruel as she wants him to be, and Haneke charts their catastrophe with the same terrifying lucidity, nightmare intensity and icy precision that marked his explorations of pathology and murder in "The Seventh Continent" (1989), "71 Fragments of a Chronology of Chance" (1994) and the awesomely disturbing "Funny Games" (1997).

"The Piano Teacher" alternates between scenes where the music (by Bach, Beethoven, Chopin and Rachmaninov as well as Schubert) exalts and exhilarates - and others where the twisted sex and psychological savagery chill you to the bone.

Because, like Alfonso Cuaron in "Y Tu Mama Tambien," Haneke shoots the sex scenes in a way that makes them seem almost unfaked, it's easy to mistake him for a pornographer. Because he doesn't flinch from the most candid and wounding emotional displays, you may even feel that he's a brute. But, like Luis Bunuel, Haneke is a moral filmmaker of true genius who delights in portraying immorality and violence - in exposing pathology, social and personal, by pushing it to extremes. You will not forget "The Piano Teacher." Nor will you forget Isabelle Huppert, a brave, brilliant actress who here plays her masterpiece.

3 1/2 stars
"The Piano Teacher"
Directed and written by Michael Haneke; based on the novel by Elfriede Jelinek; photographed by Christian Berger; edited by Monika Willi, Nadine Muse; production designed by Christoph Kanter; music by Martin Achenbach; produced by Veit Heiduschka, Marin Kamitz, Alain Sarde. French, subtitled. A Kino International release; opens Friday at the Century Centre Cinema. Running time: 2:10. No MPAA rating (adult: sensuality, language, violence, sadomasochism). Erika Kohut - Isabelle Huppert
Walter Klemmer - Benoit Magimel
Erika's Mother - Annie Girardot
Anna Schober - Anna Sigalevitch
Mrs. Schober - Susanne Lothar Dr. Blonskij - Udo Samel

Michael Wilmington is the Chicago Tribune movie critic.