"A Special Day," a new Italian movie opening today at the Outer Circle, squeaks by on the enduring skill and star magnitude of Sophia Loren and Marcello Mastroianni. The screenplay contrived for their latest reunion by Ettore Scola and Ruggero Maccari, whose contrivances grow more dubious as the story deliquesces along, can't be said to repay the stars' devotion.

Scola directed the wonderfully fanciful, flamboyant, expansive romantic-social comedies "The Pizza Triangle" and "We All Loved Each Other," written with other collaborators, the veteran comedy team of Age-Scarpelli. "A Special Day," while a smooth and in some respects clever production, is a considerably less inspired romantic fancy. In fact, it's a sweet nothing if there ever was one, a painstakingly negligible exercise in ships-that-pass-in the night poignance that suggests an Italian serving of leaves once used to brew "Tea and Sympathy" and "Brief Encounter."

The special day is May 8, 1938, declared a national holiday by Mussolini in order to celebrate Hitler's arrival in Rome on a state visit. The movie begins with an extended, fascinating newsreel depiction of this historic occasion, which recides to the background after the characters played by Loren and Mastroianni are introduced. However, it remains a noticeable, even assertive, audio background, since Scola persists in playing the tentative, intimate, plaintive notes of his love story against the strident sounds of the official radio broadcasts, virtually a musical score of portentous commentary, speeches and patriotic songs.

Following the newsreel, the camera discovers the interior courtyard of a large apartment house and begins surveying this setting, establishing the kind of gliding, inquisitive, peeping-tom viewpoint that Hitchcock used for different purposes in "Rear Window." Eventually, the camera slips through one very special window and concentrates on Loren as Antonietta, a weary Roman housewife, as she wakes her husband and six children and helps them get ready for the big day.

For the sake of convenience Scola makes his heroine the Cinderella of the building. She appears to be the only housewife not attending the festivities, allegedly due to the pressure of backed-up chores. It might have made more sense to pester her with a cold or a headache, but one is willing to allow Scola his initial contrivances, on the theory that every storyteller needs some time to get his own dishes washed and beds made.

Again for the sake of convenience it seems permissible when Loren and Mastroianni "meet cute." Her mynah bird escapes and flies across the courtyard to a perch near one of Mastroianni's windows. The hero happens to be in because he's contemplating suicide, a fate the heroine's timely interruption spares him. Nevertheless his sitaation remains desperate in the long run. Mastroianni's Gabriele, a homosexual fired from his job as a radio announcer, is destined for deportation.

The basic problem is that Scola doesn't arrange things any more ingeniously, even after the awkward introductions. If anything, he slips into a sentimental stupor. The brief encounter of Antonietta and Gabriele generates less romantic and social resonance than he hopes for, and the din of political history in the background does more to smother it than to counterpoint it.

The characters are a trifle tendentious to begin with: The romantically starved, overworked housewife and the persecuted homosexual are emblems of the humanity undervalued and spurned by a Fascist regime. Nodding her agreement with the concept of male superiority, the heroine naively remarks, "It's always men in history books, isn't it." Her new acquaintance answers, "Maybe too many; there's no room for anyone else, least of all women." She can only reply, "You're very complicated."

Loren and Mastroianni project screen personalities large and sympathetic enough to magnify the importance of the deliberately "little" people they've been asked to impersonate, at least for a while. Her limp, faded housedress, dark-ringed eyes and exhausted trudge can't conceal the fact that Sophia Loren is a splendid-looking woman and a glorious camera subject. When she checks a run in her stocking, you're too busy admiring her legs to think, "Poor soul!"

One assumes the movie will activate the beauty and vitality obviously lurking beneath the facade of household drudge. The biggest surprise - and disappointment - of the show is that Scola remains doggedly sentimental. He seems to cherish Loren as the drudge and Mastroianni as the pathetic social outcast. He's out for sustained middlebrow pathos, and nothing else - including something better, like a saucer, funnier brand of pathos - will do. The material might have avoided its unfortunate maudlin state if Scola had approached it in the raucous, screwball spirit of his earlier comedies and the sort of co-starring vehicles Loren and Mastroianni used to excel in. The characters would be genuinely endearing if they were more volatile, and set each other off in amusing ways.

Instead "A Special Day" is engineered to bring its underprivileged lovers to a bittersweet erotic consummation. This may be the most damaging sentimentality in the movie. Obviously, it grows out of the current myth that all relationships must have a sexual denouement to be authentic and rewarding, but the attitude causes more trouble than it's worth in this context.

For one thing, keeping the affair light, casual or platonic might have avoided the embarrassment of the climactic scene in which Loren places Mastroianni's hand on her heaving breast and he must register sexual indifference. Mastroianni has played impotent males in the past, and quite impressively too. Perhaps that experience confused him a bit. Playing a homosexual is no excuse for flunking the test of nature Loren poses. Instead he suggests a man with no sex drive rather than the edgy, slightly fussy character we've been watching with some interest, or the avowed homosexual the script insists that he now acknowledge to the startled housewife.

Not that this shocking revelation prevents the filmmakers from getting Antonietta and Gabriele into bed a few scenes later. Judging from their expressions, it's the most painful of ordeals. But evidently it was satisfying at some level, because Antonietta remarks, "I didn't think it could be like this." Perhaps she refers to taking the initiative, which Gabriele's passivity more or less compels her to do. On his part Gabriele confesses that it was "beautiful" but not beautiful enough to change his preferences. And that's about that.

Scola appears to be stifling his own richest talents along with the actors'. Sometimes there's no stopping otherwise capable and sensible people when they set out to be ever so tenderly and ineffably romantic. "Bobby Deerfield" is an exquisitely ludicrous example of what can emerge from such a trance.

"A Special Day" isn't that far gone, but it is a case of an exceptional director inventing down while encouraging exceptional stars to play down. What one would prefer from all of them is entertainment commensurate with their larger-than-life talents.