The new Italian import known as "The Immortal Bachelor" looks like an irresistible candidate for obscurity, and the sooner the better. Opening today at the K-B Janus, this attempt at a racy marital farce wastes the stellar quartet of Monica Vitti, Claudia Cardinale, Vittorio Gassman and Giancarlo Giannini on a scenario of lobotomizing banality.

Compared to the smirky infirmities invented to sustain "The Immortal Bachelor" by director Marcello Fondato and his hapless associates, Roger Vadim's "Night Games" was an erotic revelation and Gilbert Cates' "The Last Married Couple in America" a sparkling social satire. At least Vadim worked in fleeting nude compositions of the bountifully proportioned Joanna Cassidy and "Last Married Couple" had that weirdly gratuitous moment when George Segal, of all people, took Pauline Kael's name in vain.

"Bachelor" has one diverting bit of business: Gassman as an overextended, devious businessman answering a telephone call and cautiously pretending to be his own recorded voice. This highlight comes about two minutes into the story, so it's all downhill for the ensuing 90 minutes, which play as blithely as a lost weekend.

Vitti, cast as the most glamorous cleaning woman in recent memory, is on trial for the apparent murder of Giannini, her unfaithful, indolent yet adored spouse, who toppled into the sewer system during one of their recurrent slugfests and is presumed a goner. Cardinale, the submissive, neglected wife of shady operator Gassman, is empaneled on the jury.

The crudely manipulated idea is that the frustrated bourgeois wife will learn a liberating earful after listening to the lusty drudge describe her thrill-packed, violence-prone marriage and plead innocence with the ringing assertion, "You don't kill a man who makes love like that!"

Snobbish and dreary as it is, this class-conscious sex joke might have a wheeze or two left if Giannini, the ostensible tomcat, looked less like some scroungly little mouse the cat dragged in. The premise seems all the more fradulent and insulting for lacking a presence, comparable to the dissolute lover in "Dona Flor and Her Two Husbands," who could lend amusing authenticity to the idea that sexual gratification is basic and powerful.

Vitti and Giannini exchange resounding slaps in the alienating spirit of Lina Wertmuller's "Swept Away," where Mariangela Melato played Victor McLaglen to Giannini's John Wayne, but this punchy foreplay seems to preclude ingratiating elements of romance and eroticism.

At any rate, the vulgar lovers don't sustain enough interest to keep the continuity from drifting, let alone function as ironic rebukes or inspirations to the gentlefolk. One might invoke a might armada of screwball classics from "Roxie Hart" to "The Pizza Triangle" with which to pulverize "Bachelor," but it wouldn't justify the effort.