"I Sent a Letter to My Love" sounds like a movie to be avoided. With Simone Signoret and director Moshe Mizrahi, we see the same team that collaborated on the maudlin "Madame Rosa." A superficial plot description also tends to suggest that "Letter" must be a rather pathetic, incestuous variation on the wonderful Ernst Lubitsch-Samson Raphaelson romantic comedy, "The Shop Around the Corner." A potentially ruinous impression, since movies don't come more graceful than that.

The plot is similar; there is a certain incestuous undercurrent, and Mizrahi's pictorial style rarely transcends the pedestrian, but "Letter" turns out to be a disarming triumph anyway, especially for Signoret and her two costars, Jean Rochefort and Delphine Seyrig.

Now at the K-B Janus, this observant and appealing domestic comedy-drama succeeds in playing against the mawkish implications of its title and plot. The nominally "pathetic" characters are permitted the dignity of resourceful behavior. They're too strong-willed and funny to inspire a patronizing kind of human interest.

Signoret plays the protagonist, Louise, a spinster of 50 who has sacrificed a life of her own to care for her younger brother, Gilles, played by Rochefort. Crippled by rickets in Adolescence, Gilles is confined to a wheelchair. He and Louise still reside in their childhood home, a secluded beachfront property in Brittany left them by their parents. The introductory scenes establish an emotional bond which obviously runs deep despite their mutual frustration.

You get an inkling of the intuitive connection during the daily visit of an outsider -- Seyrig as Yvette, an absurdly coy, prim friend who runs a bakery in town and makes a habit of delivering bread and sitting down for repetitious breakfast small talk with Louise and Gilles. Annoyed by her platitudes and naivete, Louise mocks Yvette. Aroused by the same pose, Gilles flirts with her. Yvette routinely feigns shock at his presumption. Teasing her seems to be the ritual that gets Louise and Gilles started every day.

Louise mentions casually that it amuses her to read the personal advertisements in the local paper. Returning more despondent than usual from an alarming outing with her brother, who suddenly goes into a panic-stricken daze while watching his sister and Yvette ride the merry-go-round at a carnival, Louise wearily takes pen in hand and composes an anonymous personal item of her own: "Woman without children appreciating calm, affection and tenderness, wishes to meet a gentleman. . . "

In time, a correspondent replies. Signoret's reactions upon opening the letter are stunning: a sense of shock instantly complicated by an endearing, ironic humorous appreciation of the joke fate has played on her, because the correspondent is none other than Gilles. The complexity of feeling she projects at this moment is echoed later at equally intimate turning points where we watch Louise recovering from the shock of a farewell letter and an untimely arrival by Yvette. In each case she reacts with a funny delayed-action self-control, perceiving the cosmic humor of her predicament while her feelings are freshly wounded or her nerves rubbed raw.

What Louise is too sane to deny, of course, is that she's set herself up for all the maddening consequences of her attempt to relieve her loneliness. Loath to disillusion Gilles when she reads his original reply, she perpetuates a passionate hoax of a correspondence, calling herself Beatrice Deschamps, sending a fake photo and trying to keep a safe physical distance by portraying Beatrice as the sole companion of an invalid mother. Gilles is so demanding that he forces her into increasingly desperate measures, climaxed by an appeal to a professional actress to impersonate the nonexistent Beatrice on e Sunday afternoon.

The tear-jerking potential in Louise's self-sacrificing hoax is obviously enormous, but the treatment is so peculiarly unsentimental and the acting so witty that the movie never takes the fatal plunge into dampness. Louise can't be perceived as a victim when she's embodied by an actress as resilient and formidable as Signoret.

You don't necessarily associate this magnificent character actress with the voluptuous young beauty of "Casque d'Or" or even the splendidly mature, straightforward actress in "Room at the Top." Over the last 20 years Signoret has aged radically enough to seem a different screen presence, but this corpulent, wrinkled and often mournful-faced figure still has the technique and expressiveness to knock you for a loop. Moreover, she hasn't lost the directness that made her such an appealing image of middle-aged femininity in "Room at the Top." Signoret has a genius for looking at actors in a way that make any effort on their part to con her seem like a sin against nature.

Although the plot of "Letter" unfolds from Louise's point of view, denying Rochefort comparable intimacy as Gilles, his wolfish charm and range of moods -- from boyish obliviousness to somber reflection also keep his character out of pitfalls. An expert comedian, Seyrig never plays the hypocritical Yvette falsely; her Yvette just refuses to see how silly she really is.