Sandro, the protagonist of Nino Manfredi's intriguing but miscalculated marital comedy "Portrait of a Woman Nude," opening today at the Outer Circle 2, is introduced snoring at the wedding reception of his wife's sister.

While the scene may be appropriate to the story of a droopy, sleepwalking husband, it also points the movie fatefully toward an emotional dead end; it's difficult to sustain much interest in the bewilderment of an exhausted, impotent man who never really snaps out of his daze.

Manfredi, who plays Sandro, is deservedly cherished for his comic character acting in "Bread and Chocolate," "Down and Dirty" and "We All Loved Each Other So Much." In "Portrait," he is also the director, duties he took over in midstream, after he had a falling-out with the original director, Alberto Lattuada.

Manfredi directed one feature a decade ago, and there are signs of aptitude scattered throughout the wayward continuity of "Portrait" (the mellifluous, preferable Italian title is "Nudo di donna"), which he wrote in collaboration with veteran humorists Agenore Incrocci, Furio Scarpelli and Ruggero Maccari.

The setting, a chill, gray-skied Venice on the eve of the Easter carnival, is exploited for surreal strokes of humor, and there's a delirious climactic party set among revelers in costumes designed to evoke 1945; they join in such playful stunts as eating refreshments out of ration tins. The principal supporting players--Eleonora Giorgio in the dual role of Sandro's neglected wife, Laura, and the perhaps imaginary tart Riri, who looks exactly like Laura; the great French character actor Georges Wilson as an affable, aging homosexual idler; and Carlo Bagno as the sarcastic old fixture of the rare-book store managed by Laura--have far more animated and amusing showcases than the star, who doesn't seem to begrudge them the advantage.

Gracious as Manfredi may be toward his colleagues, there's something out of whack about a movie whose weakest aspect is the star's characterization. "Portrait" might have amounted to more if Manfredi seemed to be more in the picture. Sandro's disaffection is a given, without apparent provocation from Laura as Giorgio embodies her. A plebeian from Rome, a former athlete and professional racer, Sandro feels frustrated and restless in the Venetian environment that suits his wife, who can operate the bookstore, a family inheritance, without his assistance.

One rainy night after picking another fight, he walks out and takes lodgings at the spacious, decaying, leaky residence of a professional photographer, played by Jean-Pierre Cassel. Passing through a storeroom, Sandro is transfixed by a giant blowup of a slumbering nude, reclining on her stomach with her face shielded by an arm and billows of hair.

He rushes back to his own apartment to compare impressions with the sleeping Laura, who obliges by fidgeting into a position identical to the one in the photo. Back at the photographer's, Sandro can't find the blowup but jogs the memory of his host, who recalls taking such a shot of a model called Riri. This clue sends Sandro on a look-alike hunt that consumes the rest of the story and runs him ragged around the labyrinthine streets of Venice.

Riri materializes in the person of a friendly hooker, but Sandro is kept in recurrent doubt about whether she's a double or Laura in disguise. Although this confusion makes sense only as a figment of his woozy imagination--Laura's occasional ambiguous expressions aren't enough to suggest that she's a deceiver--the film makers insist on imposing a similar confusion on the audience. The movie tries to pass off the heroine's unresolved identity as a satisfying resolution: Sandro doesn't know if he's reconciled with Laura or Riri but evidently decides that it doesn't matter.

To the movie's misfortune, I think, it probably will matter. Manfredi doesn't establish the kind of interplay between fantasy and reality that allows Paul Brickman to walk a stylish tightrope in "Risky Business." Sandro is such a slug that it strains credulity to credit him with sufficient imagination to dream up a fantasy surrogate for Laura, who looks pretty desirable to begin with. (According to the script, Sandro hasn't been able to touch her for seven months, a case of impotence that would seem to cry out for clinical assistance rather than romantic comedy cures.)

Brickman creates an atmosphere in which inner lives can impinge humorously on objective reality. Manfredi doesn't provide Sandro with either an inner or outer life ardent enough to keep "Portrait" in adequate dramatic focus.