If "Somebody Killed Her Husband," now at area theaters, impressed Farrah Fawcett-Majors as a promising escape vehicle, she must have envisioned another full year of "Charlie's Angels" as cruel and unusual punishment.

Though credited to Reginald Rose, one of the most prestigious writers nurtured by television, "Somebody" is the kind of feeble trifle that would have difficulty attracting attention as a made-for-TV film. As a theatrical release, its potential looks pitifully finite.

Rose has tried to fabricate a romantic mystery in the spirit of the "Thin Man" films and such humurous who-put-that-dead-body-there? whodunits as the 1942 "A Night to Remember" with Loretta Young and Brian Aherne and Alfred Hitchcock's beguiling "The Trouble With Harry." The trouble with Rose is that he seems to be working outside his area of competence. Adept at socially conscious melodrama, he proves wretchedly superficial and expedient when it comes to inventing a diverting murder myster.

Jeff Bridges attempts to be awkwardly ingratiating in the role of the shy, effusive, feckless hero, a clerk in the toy department at Macy's in Manhattan who aspires to write children's books.

When Fawcett-Majors strolls the view while shopping with her little boy, Bridges is overcome by love at first sight. This chance encounter with his dream girl (a role Fawcett-Majors does appear uniquely qualified to embody) blossoms into an implausibly lucky affair when she turns out to possess a talent for illustration and - talk about convenient - be fed up with her husband, a greedy insurance executive.

While cuddling in the bedroom back at her apartment, the lovers are interrupted by the unexpected arrival of expendable hubbie, evidently accompanied by a guest, on the floor below. By the time the lovers walk downstairs and declare themselves, the unseen guest has departed and the husband has become a fresh corpse, sprawled on the kitchen floor with a knife stuck in his back.

Despite the trivialized approach to characterization, which causes problems from the outset, one might have played along with the movie for the sake of convenience up to the discovery of Murder Viction No. 1. When Fawcett-Majors and Bridges respond to this crisis by running about hysterically and he insists that they can't possibly notify the police, for fear of instantly being jailed themselves, a hostile glaze began to form over my eyes. The subsequent idiotic behavior of this would-be adorable couple merely thickened the glaze.

Bridges stuffs the corpse in a refrigerator and presumes to play sleuth for the next few days. Four stabbings later he has supposedly justified his folly by luring the killer into a trap. Although Bridges' calculations are meant to seem a brilliant success, it remains to be seen how grateful the authorities might be for his cavalier efforts. To be blunt, they might feel justifiably infuriated, since concealing the first homicide appears to have led to four others that might have been prevented if our hero had acted intelligently.

The lawless, antisocial impulses in a rabble-rousing, knockabout farce like "Smokey and the Bandit" may be acceptably sublimated by its cartoon fantasy stylication. "Somebody Killed Her Husband" isn't that astute. It seems to violate the line separating understandable irresponsible behavior from disgusting obliviousness. Rose's sense of the genre is so hazy that he doesn't seem to recall that it's a customary for amateur sleuths to call in the cops and then engage in running battles of wits with them. Given the nature of the story, Bridges should be an aspiring writer of whodunits rather than kids' books. Rose is so far out of it that he ends up with a hero who lacks the common decency to show a little respect for the dead.

The material requires Bridges to shoulder the acting load and keep the ludicrous plot in motion. The workload might not wear out his welcome, but the stupidity of it all certainly does. The heroine's role is so subordinate and ineffectual that it's difficutl to perceive where Fawcett-Majors and her advisers spotted a starring opportunity worth jumping at.

The movie screen is hospitable to her diminutive, streamlined, supertressy prettiness. She can look dazzingly adorable, a natural gift that gives humorous credibilty to Bridges' instant adoration.

There's also a petulant aspsect to her dream-girl loveliness that might be cleverly exploited somewhere along the line. When she gets in a pet, the rapturous spell impsed by her perky, smiling self seems to vanish. Instead of the most congenial looker on campus, one confronts the sort of peeved beauty whose sarcastic vocabulary used to begin and end with "Oh, wow!"

The supporting cast includes John Wood, Tammy Grimes, John Glover and Patricia Elliott in roles that don't begin to extend thir highly trained humorous talents. Though no worse than than "Foul Play" - and less objectionable in some respects - "Somebody" may suffer incidentally from the dark, overcast texture of its wintry New York setting. It's possible that the bright, mellow look of "Foul Play," shot in San Francisco, helped to put audiences in a depressingly receptive mood. "Somebody" seems at once witless and coorless.