A trimly crafted, engrossing thriller, "Eyewitness" always looks alert and seems to unfold with reassuring confidence. Checking my notepad after the screening, I discovered I hadn't written a single note, a sign of unflagging interest.

Nevertheless, the movie's very smoothness may set viewers up for a letdown. It's a low-key exercise in genre suspense and romance that fails to generate a high level of excitement of deliver classic dynamic thrills.

As far as I know, this is screenwriter Steve Tesich's first stab at a mystery movie. The results suggest that he maya be handicapped when it comes to contriving a satisfying example of the genre.He's not so much out of his depth as out of his shallows. By and large, movies lend themselves to the fulfilment of heroic fantasy, but Tesich keeps letting real life intrude on his fantasy life.

As defects go, this one is certainly novel, even ingratiating in a counter-productive sort of way.The characters get more humanizing touches and complicating motives than most of them actually need to function adequately as pawns in a basically trumped-up story calculated to generate tension and excitement. Indeed, the realistic tendencies weaken many of the fabricated threats and perils. For example, Tesich can't really get the full sinister value out of an assassin willing to poison the hero's pet dog if he's also determined to portray the assassin as a man with a mission who has a noble side coexisting with a ruthless side.In this artificial context, it's not playing fair with the audience to invite a simple, satisfying enmity and then turn around and remind us that everyone has his reasons.

Tesich has been candid about the fantasy life that nurtured "Eyewitness" up to a point. The hero is admittedly Tesich's alter-ego, inspired by summer jobs as a night janitor in Chicago office buildings and a crush on TV newscaster Lesley Stahl. Relocated in Manhattan and given the deceptively wimpy name Darryl Deever (rhymes with Bucky Beaver), the hero is foxily impersonated by William Hurt, the foxy introverted type who also plays the lead in "Altered States."

Darryl fears that his buddy and prospective brother-in-law, Aldo, played by James Woods, may be implicated in the murder of a sinister Vietnamese businessman who has offices at the building where both young men work as night janitors. While trying to shield Aldo, Darryl places himself in jeopardy by implying that he knows more about the killing than he does. This deception is designed to intrigue a glamorous TV reported named Tony Sokolow (Sigourney Weaver in her first movie role since "Alien"), whom he has been admiring from afar, even taping her appearances for leisurely contemplation after returning home from work.

The conventional romantic idea is that good-guy Darryl, a tough and resourceful plebeian, succeeds in ingratiating himself with Tony, a Jewish patrician celebrity involved with an elegant but disturbing Israeli agent played by Christopher Plummer. The love affair ripens, more or less implausibly, against a background of international intrigue, eventually resolved by tying together subplots.

Tesich's case for Darryl and Tony rests on wishful thinking. Hurt isn't without charm, in his peculiarly withdrawn way, but at the very least he would seem to need more eloquence to charm Tony into intimacy. It seems odd that Tesich can't fake an acceptable line for him. He did much better by the adolscent hero of "Breaking Away." Darryl's expressiveness never transcends halting professions of hopeless infatuation. You're left with the disquieting impression that his personality might be better suited to another stereotype, the solitary lovelorn psycho with designs on the heroine.

Director Peter Yates demonstrated his flair with the genre several years ago in "Bullitt," but there's nothing in "Eyewitness" that threatens to rival the gratuitous but satisfying spectacle of his car chase over the hills of San Francisco. A change-of-pace reunion for Yates and Tesich, who collaborated on the endearing "Breaking Away," "Eyewitness" also fails to match the kinetic high points of that film's bicycle-racing sequences, although it belongs to a more transparently manipulative genre.

A number of subsidiary elements also remain to be effectively integrated. Hurt has scenes with Woods, with Pamela Reed as his frazzled girlfriend and with Kenneth McMillan as his gruff, crippled father that evoke funny kinds of intimacy, but they seem to belong in a movie like "Breaking Away," or perhaps the upcoming "Four Friends," an autobiographical Tesich script directed by Arthur Penn. They're authentic interludes from a different esthetic realm -- a keenly felt life that is irrelevant to the effectiveness of "Eyewitness."

It's not inconceivable that they could be blended with calculations that were strictly for ominous kicks, but at this stage Tesich hasn't mastered the recipe. "Eyewitness" is a movie that might be better if it were a bit trashier. Tesich and Yates are trying to do a class act on a premise that would go further on artful cunning and an uncomplicated dedication to putting moviegoers on the edges of their seats.