"Wifemistress," the preposterous new Italian film at the K-B Janus, cries out for a kickier silly title: "A Wife's Revenge" or "I, a Wanton." A softcore porn reverie about a sheltered wife who swaps lives with her neglectful libertine husband, "Wife mistress" is a shamelessly fattening repast whipped up by director Marco Vicario and assistant chefs like cinematographer Ennio Guarnieri and composer Armando Trovaioli.

Given the fundamental worthlessness of the story, the filmmakers need all the decorative camouflage they can scrounge up. Their efforts don't transform "Wifemistress" into an indispensable bad movie, but they make it a bad movie you might enjoy idly wallowing in.

The setting is an unspecified provincial town at the turn of the century. Luigi De Angelis, played by Marcello Mastroianni, is a prosperous wine merchant who spends most of his time on the road, presumably pursuing business. His estranged wife Antonia, played by Laura Antonelli, spends all her time in bed, immobilized by a psychosomatic paralysis invented in retaliation for her husband's neglect.

We discover that Luigi is dabbling in radical politics. This avocation leads to a shooting in which Luigi is mistakenly identified as a murderer by the victim's child. Luigi goes into hiding, holing up in an abandoned, shuttered loft directly opposite his own house. Antonia, jumping to the conclusion that her husband is dead, also jumps out of bed for the first time in years. Assuming responsisibility for the business, she takes over Luigi's delivery route and then acquires a taste for his secret activities, radical political agitation and uninhibited sexual experimentation.

Thanks to the proximity of his hiding place, Luigi can torment himself day after day peeking at the newly aroused, independent Antonia. He grows so despondent that he refuses to come out of hiding after the real murderer confesses. Luigi remains in the loft to spy on Antonia and cultivate his humiliation in solitude. Ultimately, she gets wise to his presence and makes him squirm even more by entertaining admirers of both sexes in front of his sorrowfully fascinated eyes.

This revenge plot has swell comic possibilities, some of which surface despite Vicario's attempt to keep a straight face and impose a luxurious, languorous mood of eroticism. For example, there's no way to prevent Mastroianni's voyeuristic gazing from looking funnier and funnier as Antonelli accelerates the erotic pace.

In typical pornographic fashion the wronged wife's liberation is equated with imitating her husband's domineering and licentious behavior. In less enlightened but possibly more dignified times the pretense of tit-for-tat would have been enough to put an erring but still valued mate in his place. What will become of Luigi and Antonia after such a ludicrous reconciliation? Only the Letters column of Penthouse could do justice to the next phase of their dizzy union.