In "The Man Who Wasn't There," a 3-D film now at area theaters, Canadian actress Lisa Langlois transcends potentially humiliating, silly circumstances to ingratiate herself in a disarming fashion.

As the loyal and intrepid heroine Cindy Worth, Langlois comes to the aid of the hero, Steve Guttenberg, who is a minor State Department functionary named Sam Cooper, when far-fetched events conspire to turn him into an invisible fugitive on his wedding day. Minutes away from marrying Cindy's peeved older sister Amanda (Morgan Hart), Sam paces around a room at the Hay-Adams in boxer shorts adorned with heart designs while awaiting a suitable change of clothing. His sanctuary is invaded by an invisible man on the run from pursuers who soon arrive, knock Sam unconscious and eventually succeed in killing their prey by hurling knives into his back. This also provides the pretext for the most alarming 3-D illusion in the picture, since the knives are aimed between the eyes of the audience members.

The killers are obliged to beat it before they can take possession of the McGuffin, a silver sphere that contains several miniature vials of a blue liquid that produces invisibility when ingested. The dying victim entrusts it to the woozy hero, who then flees impulsively when friends and authorities enter the room. With the sphere tucked precariously into his shorts, Sam scampers around the ledges and corridors of the Hay-Adams until he can improvise an exit in a bellboy's uniform. His fiance'e refuses to have anything to do with him, but Cindy comes through like a champ; in the course of ducking assorted pursuers and blundering to the bottom of what proves an exceedingly shallow mystery, Sam and Cindy emerge as the genuine love match.

The invisibility gimmick demands things of the leading lady that make it easy to understand why the role might be scorned by actresses who value their dignity and enjoy the luxury of choosiness. Nevertheless, Langlois demonstrates how a good figure and good humor can combine to finesse an assignment that flirts with lewd embarrassment. To avoid detection, the hero and heroine occasionally resort to the secret potion, which renders only flesh and bone invisible, so . . . to disappear altogether, they must get rid of their clothing. These little details set up irresistibly absurd images like the sight of Sam's shorts running down the street or Cindy draped in strategically placed vines after a chase through the zoo, where she has suddenly returned to visibility in sight of two police officers.

Langlois gamely surmounts an extended romantic interlude that subjects her to even trickier booby traps. She and Guttenberg are supposed to steal an evening of erotic bliss while his character remains invisible. Required to warm to the advances of a disembodied voice, Langlois is able to exploit the ridiculousness of it all to her advantage.

A dynamic young comic presence in both "The Chicken Chronicles" and "Diner," Guttenberg doesn't enjoy the same opportunity in "The Man Who Wasn't There," where he's frequently obliged to be there in voice only.

The movie begins with one of the sorriest slapstick situations I've ever cringed through--a food fight breaks out at a State Department reception among the hero's diplomatic charges, representatives of Third-World countries so puny that they're shunted off to a separate, cheapskate dining area. Director Bruce Malmuth, whose only previous theatrical feature was the police melodrama "Nighthawks," handles this ugly brainstorm with all the finesse of a maddened water buffalo.

The 3-D photography also settles down as the movie proceeds, exchanging a lot of garish shock effects and eyeball-punishing lateral movements for an emphasis on forward and backward tracking shots. These produce an especially effective mood of suspenseful mobility during a passage when Sam and Cindy edge along the rooftop at the Washington Boat Club. The process seems to wash out color as much as usual, but the light level remains well above the Black Hole of Calcutta standard that plagues most 3-D features.

"The Man Who Wasn't There" also uses more of the city than I anticipated, some of it in the hilariously illogical way that often gives movies shot in a familiar locale an unintentional element of humor. For example, Sam gets from his State Department reception to his Hay-Adams wedding date by a roundabout route that includes a detour through Georgetown for the purpose of recking a car at the flower shop on Wisconsin and N. Unless my eyes deceived me, Washington also gave way to Beverly Hills and other strangely Californian settings in certain car shots. "The Man Who Wasn't There" often looks like the work of filmmakers who didn't know where they were. THE MAN WHO WASN'T THERE

Directed by Bruce Malmuth; original screenplay by Stanford Sherman; produced by Frank Mancuso Jr.; Eric Van Haren Noman, camera operator and 3-D consultant; effects supervised by Eric Brevig; production designer, Rob King; filmed at Zoetrope Studios in Hollywood and in Washington, D.C. Rated R. THE CAST Sam Cooper....Steve Guttenberg Ted Durand....Art Hindle Amanda Worth....Morgan Hart Cindy Worth....Lisa Langlois Boris Potemkin....Jeffrey Tambor