The erstwhile filmmaking prodigy Marco Bellocchio hasn't enjoyed a celebrated or prolific career, but judging from "Leap into the Void," opening today at the K-B Janus, he's remained consistently and obsessively distinctive. In 1965 Bellocchio was linked with Bernardo Bertolucci as a one-two punch of gifted young Italians. At the same improbably tender age, 25, they made more or less simultaneous splashes, Bellocchio with a first feature called "Fists in the Pocket" and Bertolucci with a second called "Before the Revolution."

The legitimate artistic successor to the great Spanish surrealist Luis Bunuel, Bellocchio has a grotesque genius for expressing the irrational.

The opening image of "Leap into the Void" provides a stunning, deadpan example. Michel Piccoli appears at an open window and stares down at something or other, his head cocked to the side in an unaccountably funny, alarming way. The object of his gaze is soon revealed: the draped, blood-spattered remains of an apparent suicide victim, presently identified as a desperate young woman who may have been goaded over the precipice by a vicious boyfriend. The movie attempts to account for the demented psychology that leads Piccoli, a judge named Mauro Ponticelli, from a place of observation above some anonymous suicide to a suicidal imperative of his own. In a single economical stroke the opening composition launches the story and foreshadows the denouement. Symbolically, the entire movie is summarized in the first shot.

At first glance Judge Ponticelli appears to be coping bravely with a controllable heritage of family lunacy. He lives in a gloomy, antiseptic Roman apartment, caring for a strangely melancholy, preoccupied woman who turns out to be his unmarried sister Marta (Anouk Aimee), whose ordinary hysteric tendencies have allegedly intensified with the approach of menopause. From Mauro's standpoint, Marta appears to be a constant source of anxiety, muttering to herself and cutting his dinner steak in a funny pattern and threatening to attract the attention of the neighbors by screaming or chucking things out her bedroom window.

The joke of the presentation is that it grows more and more obvious that poor Mauro is going quietly, fussily cuckoo. Marta may indeed need plenty of looking after, but her watchful, frustrated brother is cracking up as a consequence of his deeply resentful guardianship. The offhand indications that Mauro may be worse off than Marta are confirmed when he clumsily tries to promote a murder conspiracy. After interviewing the nihilistic young crook (Michele Placido) who may have provoked the suicide to her death, the judge tries to cultivate the acquaintance and encourage him to try his ladykilling skills on Marta.

While he's far too squeamish to hurt Marta himself, Mauro intimates that he'd certainly appreciate a helping hand from someone ruthless, like this predatory representative of the younger generation. "All my life there's been someone babbling in the next room," Mauro confides. "Many people say they want to kill themselves, but somehow they never do . . . I feel as if they've pulled my leg."

A defective plot manipulator, Bellocchio excels at the deliberate, droll accumulation of details that simply illustrate Mauro's descent into lunacy. He's at his best when he seems to be assembling a dossier of madness, and the stuff he shows often has a perversely funny originality and authenticity. For example, when Mauro mumbles a prayer of some kind to himself while watching Marta try to jaywalk across a busy street, you can't be sure whether he's pleading for her to avoid or incur injury. Probably both, given the state of his agitation at the time. The movie is full of this kind of perception--not exactly desirable but psychologically convincing. When Bellocchio evokes the subconscious, the evocations have a disturbing, witty eloquence. It may not be wholesome imaginative territory in there, but he seems to be intimately familiar with its warped landscapes.