In my vehemently prejudiced opinion heaven must rejoice every time a Robert Stigwood production lays an egg. The appearance of "Moment by Moment" should provoke the jolliest havenly uproar since "Sgt. Pepper's Lonely Hearts Club Band."

Opening today at area theaters, "Moment by Moment" is a Grade-A stinker, hatched under Stigwood auspices for the greater mortification of Lily Tomlin and John Travolta, locked in excruciating erotic two-step as a melancholy Beverly Hills housewife and her hopeful lover boy.

On the current kitsch market, "Moment by Moment" lags behind "Slow Dancing in the Big City" but easily outstupefies "Oliver's story." It would be fun to double-bill "Slow Dancing" and "Moment by Momeny." since they masterfully illustrate the contracts between Manhattan and Hollywood taste in romantic drivel at this wacky point in time.

With a little hard-core elaboration and styling, the "plot" of "Moment by Moment" could fit snugly into one of Nancy Friday's collections of women's sex fantasies.Asked to conjure up a dream lover, your average bored and restless fantasist might indeed flatter her vanity by identifying ecstacy with a gigolo who looked exactly like John Travolta.

Down in the dumps because of her husbahd's infidelity, the heroine takes up residence at her Malibu retreat to brood in privacy. A young man who claims to have parked cars at one of her parties strikes up an acquaintance. She tries to brush him off, but he keeps hanging around. His persistence eventually pays off, and they become lovers. But can the heroine step out in public with her new romance without feeling scandalized?

The circumscribed nature of Jane Wagner's screenplay and the hazy nature of her direction tend to divorce the film from any semblance of reality, both social and erotic. For all practical purposes "Moment by Moment" is a two-character idyll, concentrated at a location-the heroine's Malibu Colony beachhouse-that seems imaginary.

Listening to Tomlin and Travolta exchange tender banalities on the veranda, your attention drifts away to the Dolbyized sound of murmuring waves and you feel mightily tempted to stretch out and nod off.

Wagner and Tomlin made their reputations collaborating on comedy material, but it appears that even professional funnywomen lose their comic perspective when stooping to genteel sex fantasy designed to massage a mass audience into swoony slumber.

Wagner and Tomlin should have balked at the very names of the lovers: Trish and Strip, as in Sunet Strip. Instead they seem to be anticipating national palpitations when Tomlin sighs, "Oh, Strip" or "Mmmmmmmm" at Travolta's hunky nearness.

During the sublimely ridiculous hot tub sequence, when Travolta slips off his bikini trunks just out of camera range and Tomlin, already immersed, throws him a long, lustful glance from under her sleepy eyelids. "Het's smoke some pot," she suggests insinuatingly. Scenes like this create a strong presumption that the pot has already been smoked.

Tomlin and Travolta are also a preposterous romantic match on the face of it. They look so much alike, especially in profile, which emphasizes the affinity between their long faces and wavy, backswept haircuts. It's as if Trish had conjured up a phamtom lover in her own image.

Tomlin first appears doing the aimless walking scene immortalized by Jeanne Moreau in "La Notte." Trish's turf is Beverly Hills, and Wagner superimposes the names of smart shops over her heroine as she trudges along. After associating names like Gucci, Bijan and St. Laurent with Trish, you waint breathlessly for Wagner to label Travolta's street kid. He appears to get Hamburger Hamlet and Schwab's, but you can't be sure. Maybe he's just passing Hamburger Hamlet, and he and Trish are destined to bump into each other at Schwab's.Certain early remarks by the characters become reliable cues to their mentality. Zombie Irish asks her druggist, "What about the sleeping pills? I'm gonna be at the beach for a while and I need a good supply." Trying to ingratiate himself with his prospective patroness, Strip confides, "The only reason I scored these reds is because I hoped it would open up a line of communication to you."

Although Strip seems to make a point of hanging around Trish until she can no longer resist his inviting torso and supplicating glances, he gets on high high horse when she just wants to mess around. "When you're ready to admit you can love me, you can have me," he pouts. "If you're not ready to commit to a meaningful relationship, forget it. I'm through with cheap sex."

Again, you think Wagner and Tomlin, who specialize in funny stuff, have to be kidding, but this drivel is meant to be taken in deadly earnest. The story might have had a dramatic focus if Strip had been characterized as a kid gigolo torn between a young woman and an older woman. Christopher Walken distinguished himself in "Roseland" portraying a character in just such a situation.

"Moment by Moment" may have doomed itself commercially by failing to give Travolta's adolescent feminine following a surrogate to identify with. Are the teen-agers who throbbed to "Saturday Night Fever" going to be thrilled watching Lily Tomlin fuss over their dreamboy?

Travolta tries to brighten up this fiasco with the personality resources at his disposal. In the beginning he's got his amiably goofy smile to rely on. At least he's trying to be likeable, in merciful contract to Tomlin's inexpressive, somnambulistic Trish. When Strip must expose his sulky, clingy needs, it's all over for Travolta too.

Talk about a meteoric career! From "Saturday Night Fever" to "Grease" to "Moment by Moment" in only a year. Things can only look up for him again after "Moment by Moment." C4