"Birgitt Haas Must Be Killed," a new French import at the K-B Janus, is an exorbitantly dreary example of the maudlin espionage melodrama.

The film also would appear to be at a competitive disadvantage arriving immediately after the telecast of "Smiley's People," since it resembles nothing so much as '60s John le Carre' warmed over by drab French imitators.

Birgitt Haas is the name of a notorious German terrorist, still at large in Munich but subject to constant surveillance by government agents who've insinuated themselves by becoming her casual sex partners. For reasons that are never satisfactorily explained, the Germans turn to a clandestine French agency, headed by Philippe Noiret, which specializes in assassinations contrived to suggest accidental death, in order to formulate a nasty but effective scheme for obscuring the execution of Haas.

Noiret authorizes a plan that seems dubious. The idea is to exploit Haas' promiscuity by setting up a chance encounter with a French patsy, a despondent cuckold played by Jean Rochefort, who will presumably end up in her bed, allowing a professional assassin to sneak in, kill her and frame the hapless stooge for murder.

This master plan seems to be riddled with troublesome complications, but it's undeniably unsavory and might be expected to suffice in the hands of filmmakers shrewd enough to manipulate it for tawdry suspense.

Unfortunately, director Laurent Heynemann and his screenwriting collaborators prefer to approach a shaky thriller premise in the guise of rank, soggy-sleeved sentimentalists. For example, while we're invited to confuse Birgitt Haas with a real-life revolutionary desperado like Ulrike Meinhof, she is played by the sad-eyed, timorous, melancholy Lisa Kreuzer, and the dreaded Birgitt quickly invalidates her reputation by coming on like a sorrowful angel. She's even introduced in church, seeking the counsel of a priest and using his apprehension as a pretext for moral one-upmanship. When she alludes to her criminal career later, we're left with the impressions that her motives were always honorable and her methods defensible and that she's merely the victim of a monstrous frame-up. "Our targets had a meaning," she sighs. "They blame me for targets I know nothing about."

Heynemann doesn't confine the hearts-and-flowers solicitude to Birgitt alone. Noiret the dirty trickster and Rochefort the dupe also emerge as wildly improbable saints. Together they constitute a downright sickening trinity of holier-than-thou degenerates. Despite his professional status, Noiret is studiously conscience-stricken. We can't help noticing he's made of finer stuff than the ambitious underling who concocts the Haas caper for him or the mandarin superior, fond of oriental dressing gowns and electric train sets, who foists the unpleasant assignment on him in the first place. Noiret is even so close to his wife that he discusses presumably secret company business with her.

Birgitt and the patsy not only hit it off, they share an instantly redemptive great romance, cruelly interrupted of course by the nefarious matchmakers. Birgitt is left unkilled when their original plan goes awry, so Heynemann leaves us with the inspirational thought that Rochefort will be waiting faithfully if and when his beloved returns from incarceration. Unlike Sam Spade, he seems perfectly sincere in his assurance of constant devotion to a trigger-happy sweetie. Noiret, one gathers, would be proud to make amends by acting as Rochefort's best man.

The awful truth is that "Birgitt Haas" would be substantially improved if it took a cold-eyed view of its characters -- if, in fact, it were as enjoyably cynical about ruthless and culpable types as "The Maltese Falcon."

Quite apart from the lack of dramatic justification, the sanctimonious approach guarantees a less entertaining form of thriller.