Men are invariably the butt of the joke in the intuitive, exploratory sex comedies written and directed by Bertrand Blier, the most inimitable of filmmaking humorists. Moreover, the joke seems to be cosmic in origin.

There's no getting around it, whether your temperament is aggressive or passive, your status respectable or criminal, your intellect cultivated or brutish: When you get right down to it, there is no creature as superfluous and vainly self-deluded as the adult male.

Blier repeatedly contemplates the hilarious gulf that separates a man's sense of self-importance from his real insignificance in the larger scheme of things. "Beau Pere," opening today at the Key, is an exquisitely deadpan variation on this theme.

Remy Bachelier, the absurdly twerpy, overmatched protagonist, is a melancholy nonentity, a pianist employed to provide pleasant background music at a posh restaurant. Confiding in us directly while tickling the ivories, Remy observes that no one listens to him, "so I played for myself, trying to get the phrasing right and never making it." The proper phrasing seems to elude him in other byways of life too. Trying to patch things up with his dissatisfied mistress of eight years, Martine, he points out that "things evolve--for instance, I used to turn you on. . . ."

Fate solves the impasse between Remy and Martine when she dies in a car crash. However, this fatality confronts him with a fresh series of bungled challenges, beginning with the obligation to break the bad news to Martine's 14-year-old daughter, Marion, and culminating with the need to resolve the ambiguities of their relationship. At first Remy imagines that he can be mother and stepfather to the poor orphan, who refuses to live with her natural father. When Marion professes her love for Remy, "dear dad" begins weakening to the point where he becomes putty in her precociously demanding hands.

Patrick Dewaere, who achieved a marvelous stoogey rapport with Gerard Depardieu in Blier's "Going Places" and "Get Out Your Handkerchiefs," must sustain a stoogey solo in the role of Remy. He's blissfully funny, so withdrawn into overcivilized passivity and wimpiness that one begins to think of Remy as some bizarre new breed of eunuch. Dewaere affects a dreamy, dopey expression around the eyes and looks creepily young. It's as if the character were returning to pubescence.

Remarkable as this caricature of ineffectual masculinity appears to be, it also poses dramatic problems that can't seem to be finessed in the mysterious, intuitive style Blier perfected in his earlier films. The story comes full circle, and there's a dazzling kicker, but the calculations seem faulty. I'm not sure Blier himself is comfortable isolating the character of Remy, because Maurice Ronet as Marion's father tends to hover tentatively on the outskirts of the scenario, suggesting a fresh partnership of baffled males that never quite materializes. It probably would be more effective if the girl's impulses kept mystifying both her well-meaning, oblivious "fathers."

The real stickler in "Beau Pere" is Remy's passivity. Dewaere makes him such a consummate twit that Marion's girlish passion for Remy begins to look plenty cuckoo. Unfortunately, the misconception on her side is an aspect that Blier seems to overlook. As usual, it's the masculine style of obliviousness that preoccupies and bemuses him. He hasn't anticipated that his Lolita's attraction to his reluctant Humbert Humbert might end up defying belief and therefore require further explanation.

Blier, a devastating satirist of male sexual vanity and ignorance, has never pretended to be a mind reader where women are concerned. "Beau Pere" happens to evolve in a direction that may have obliged him to make a wild guess or two. Since Remy may be the Wimpy Modern Male par excellence, I can't help wondering what makes him romantically fascinating to a kid as allegedly precocious as Marion