"Last Embrace" is a romantic murder thriller with a stylistic verve that should allow moviegoers to forgive its plot deficiencies.

Directing his first theatrical feature since "Citizens Band" Jonathan Demme has orchestrated a deft production in the film noir tradition of the '40s. But it runs out of suspects and ingenuity about a reel early.

Roy Scheider stars as a government agent whose wife is accidentally killed while he's on an apparently routine assignment in El Paso. After a nervous breakdown and three months of therapy at a sanitarium on Long Island he returns to work and discovers that he may be considered expendable.

His usual contact, a department store employe played by Marcia Rodd, has no new assignment for him. His superior seems openly hostile. A former colleague is stalking him. His apartment in New York City has been sublet to a voluble, awkwardly appealing graduate student in paleontology from Princeton - an ambiguous role played with astonishing, career-reviving with by Janet Margolin.

Scheider turns out to be a marked man. The mystery revolves around the discovery of precisely who has it in for him. After pointing the finger of suspicion explicitly at his employers, the plot switches suspects in mid-stream to a psychotic killer engaged in a vendetta inspired by events that occurred two generations earlier in the ghettos of the city.

The plot simply won't stand up to analysis. Since the killer is definitively identified with plenty of running time remaining, it takes all of Demme's skill and a cliffhanging finale at Niagara Falls to prevent the movie from deflating catastrophically. Fortunately, "Last Embrace" is so expertly visualized and performed that Demme finesses the structural weaknesses. Always on the move with vivid, dexterous imagery, demme and cinematographer Tak Fujimoto make the film constantly exciting and amusing.

The playful, dynamic look of the movie itself is anticipated in Pablo Ferro's elegant credits, which make a game out of misdirection, entering the frame from left and right, high and low, top and bottom. It's evident from Miklos Rozsa's moody score and Ferro's graphics that "Last Embrace" grows out of a genuine affection for certain thriller traditions.

Fujimoto's springly, streamlined camerawork is especially effective at creating excitement or amusement in lateral motion. This is easily the best-looking American movie since "The Warriors." "It also happens to be a more agreeable sort of gratuitous thriller than either "The Warriors" or Brian De Palma's "The Fury," which exaggerated their dramatic defects by shooting for fantasy and supernaturalism.

The faulty plot of "Last Embrace," presumably transposed by screenwriter David Shaber (who also worked on "The Warriors") from Murray Teigh Bloom's original novel "The Thirteenth Man," at least keeps its feet on the ground. Demme's fondness for the interplay of actors in a humorous, naturalistic style also enhances the movie's pleasures.

There's a wonderful string of supporting players: Jacqueline Brookes as a therapist, Rodd as the saleswoman, Christopher Walken as the evil-looking boss, Charles Napier as a menace, Sam Levene as a elderly sleuth, David Margulies and Lou Gilbert as rabbis, Andrew Duncan as an ill-fated philanderer and, best of all, John Glover as Margolin's personable, apprehensive suitor.

Scheider and Margolin contribute striking portrayals in the leading roles, although it appears that they're prevented from developing a compelling romanic relationship by the shallow twists built into the story. Although Margolin's herself as a suspicious figure by occupying Scheider's residence, Margolin makes this bookish interloper so disarming and eccentrically likable that it's disappointing to see Scheider keep up his defenses.

As in "Jaws II," Scheider occasionally teeters on the verge of Kirk Douglas excesses when projecting a haunted personality. He doesn't go off the deep end, though.

Nevertheless, he imposes a flinty, implacable presence that Margolin can't seem to break through, even at her most adorable. The movie seems to be thwared in part by Scheider's reluctance to unclench his performance.

"Last Embrace" is too flawed to be remembered as a classic, but it falls short in a consistently entertaining, attractive style. CAPTION: Picture, Janet Margolin and Roy Scheider in "Last Embrace"