"Without a Trace" leaves a shallower imprint than it ought to after presuming to examine a primal anxiety--parental anguish over the mysterious disappearance of a child. Opening today at area theaters, this effective but inescapably genteel and placating suspense melodrama shies away from the gut-wrenching intensity of emotion suggested by its premise.

The first feature directed by Stanley Jaffe, whose successful producing career peaked when "Kramer vs. Kramer" monopolized the Oscars, "Without a Trace" is content with a commercially streamlined approach to a topic that might be better served by ruthlessly messy but revelatory emotional realism.

Ostensibly, the movie depicts a mother's ordeal. Susan Selky, played by Kate Nelligan, is identified as a lecturer in American literature at Columbia. Recently separated from her husband Graham (David Dukes), a fellow academic who evidently finds coed temptation irresistible, the heroine resides with her 6-year-old son Alex in an affluent and seemingly secure Brooklyn neighborhood. On a perfectly ordinary but obviously fateful weekday morning Susan wakes Alex, fixes his breakfast and watches him walk around the corner, headed for a school within two blocks of their town house, before leaving to make her own class.

When she returns later in the day, Susan learns that Alex never completed that short walk to the schoolhouse. He vanished, and it must have happened mere moments after he left her field of vision. The most powerful and haunting image in the movie is that impression of the little boy as he disappears from his mother's watchful gaze. It evokes precisely the irrational twinge you feel whenever seeing a child off. In this story, of course, the heroine is destined to see a terrible apprehension realized. This was the day when it would have been better to trust every superstitious nerve in her system and never lose sight of her child. Once the disappearance is confirmed, Susan's distress is magnified by the public, institutional repercussions of the tragedy, as the police set up a command post in her home and the media and curiosity-seekers congregate outside.

The movie attempts to depict this turbulent, painful aftermath in a systematic, coherent fashion, touching on a variety of appalling aspects, such as the proliferation of crank calls and letters, the humiliation of public appeal and exposure and potential manipulation.

The filmmakers have no intention of risking commercial failure by keeping the case unsolved, although similar cases in the thousands remain unsolved in real life. The commitment to a reassuring, tear-jerking denouement would seem less trite and opportunistic if "Without a Trace" were simply prepared to probe more deeply into the ordeal it outlines, introducing many gripping possibilities without sustaining a dramatic grip on any one of them.

The source material, a novel by Beth Gutcheon called "Still Missing," is unfamiliar to me, so I'm not certain if the story was thinly dramatized from the beginning or simply shrank in the process of movie adaptation. Whatever the problem, "Without a Trace" provides little sustenance. It keeps serving up overprepared tidbits of torment when you'd prefer to get down to a main course. Jaffe's inexperience is no doubt a considerable stumbling block. His direction shows an emotionally inhibiting, flattening kind of reserve.

For example, Nelligan gets a scene where she sobs quietly to herself in a bathtub. Conceptually, it's already too close to one of Diane Keaton's best scenes in "Shoot the Moon," but the situation itself is certainly defensible and Nelligan's orchestration adequate. The problem is that you can anticipate every emotional gesture the scene is calculated to make. It's not as if the actress is doing anything wrong, but nothing she does takes you by surprise, provokes a response you hadn't been prepared for.

This weakness is endemic. When Jaffe begins orchestrating an episode, you invariably feel as if you can skip ahead to the payoff long before the director arrives there. When Nelligan tries to blot out things by concentrating on a piano piece or when she becomes embroiled in arguments with her husband or best friend, the effects remain tediously banal and predictable. Jaffe's depiction of the comforting domesticity enjoyed by Judd Hirsch as Al Menetti, the police detective in charge of Alex's case, reflects an identical ponderous sincerity. Al cares a lot, and Jaffe doggedly underlines his concern by observing him look in on his own little boy and discuss the case with his nice wife. Again, none of this is inherently false or superfluous. Jaffe merely makes it appear burdensome.

The inadequacies and miscalculations tend to accumulate and nag at you as the plot unravels. For example, the movie needs more mother-son interplay in the opening sequence and perhaps a better explanation for why Alex seems to be such a docile, phlegmatic specimen of a little boy. Nelligan also evolves into a curiously self-controlled, stalwart image of distressed maternity without at the same time being entrusted with the decisive action leading to the recovery of her son. In retrospect the leading actress seems clearly shortchanged in terms of both eloquent suffering and heroic action.

Having liked much of Nelligan's previous work, I'm a bit reluctant to admit that I don't really find her very persuasive as the embattled mother. She seems a little detached from the nature of the anguish one is supposed to share in this story, and I suspect that audiences may find it difficult to warm to her somewhat standoffish, overgroomed presence, which suggests unfortunate affinities with the Mary Tyler Moore character in "Ordinary People." She's also been handicapped by a fashionable hairdo that looks distracting rather than flattering or merely appropriate to the character. Stockard Channing, cast as her best pal, also flaunts too much hairdo. I'm not on confident esthetic ground here, but I suspect that something is amiss when the hair styling keeps diverting your attention from what key characters are supposed to say and feel.