Michael Crichton's trim, tense movie version of "Coma," opening today at area theaters, represents a considerable improvement on its literary source, a recent best-seller by Robin Cook, a Boston ophthalmologist trying his hand at a thriller for the first time.

Crichton has supplied the editing and streamlining that the book urgently needed. "Coma" was obviously meant to attract filmmakers, and Crichton, the former doctor who wrote "The Andromeda Strain" and "The Terminal Man" and made a promising directing debut three years ago with "Westworld," was probably the ideal young filmmaker to handle this scare story with a medical setting.

Dr. Susan Wheeler, a slightly testy surgical resident at a Boston hospital, begins to fear foul play when one of her best friends fails to regain consciousness after an apparently minor, routine operation. Nosing into hospital records, she discovers several cases of brain death suffered by young, healthy patients while under anesthesia during minor operations. Her snooping eventually leads her to a bizarre caretaking facility for the comatose. It also places her life in jeopardy, since her suspicions are justified: The "accidents" have resulted from a criminal conspiracy.

Crichton's first astute move was transforming Wheeler into a somewhat older woman with a little more authority. The heroine in the novel was a first-day intern who began demanding explanations from her superiors before she's been introduced to them. The movie heroine is granted some professional standing at her institution before she takes up freelance sleuthing.

Crichton's second astute move, the casting of Genevieve Bujold as Dr. Wheeler, places an intriguing and resourceful actress at the center of the suspense mechanism. Bujold isn't the herione envisioned by Cook -- a 23-year-old dish -- but she makes much more sense as a tenacious professional without ceasing to be an appealing focus of human interest.

Bujold enters in a surprisingly defensive, irritable mood, bickering over domestic chores with boyfriend Michael Douglas, cast as a fellow resident who makes most of the conciliatory gestures in their relationship. As a rule, heroines tend to come on softer and thrillers tend to come on mellower. Both the star and the movie display taut, edgy characteristics from the outset. Bujold confessed that she was a bit worried about this approach, which leads her to believe that Dr. Wheeler will never end up living happily ever after with Douglas' Dr. Bellows, but she gets the opportunity to multiply her character's moods without betraying her pride or determination as the plot unfolds.

Crichton doesn't modulate his tone. He puts you on edge and keeps you there. His style is incisive and gripping, but it may be too neat to release as much tension as he succeeds in building up. Crichton tends to short-change his payoffs after setting us up adroitly. He isn't playful enough to squeeze the last ounce of suspense from climactic episodes, even when they deserve to be squeezed.

The heroine is obliged to save her skin in surroundings one doesn't encounter every day: a refrigerated locker full of hanging cadavers and a labyrinthine laboratory full of compatose bodies suspended from the ceiling by life-support lines. These settings are marvelously eerie, and the heroine handles herself with admirable ingenuity, but Crichton remains a little too reserved to capitalize on his own best effects. He resists pressing the advantage even when you want him to.

It's too early to tell if Crichton is a fundamentally cool customer or a capable, wary filmmaker playing it close to the vest because he's still relatively new to the trade. For one reason or another he isn't quite prepared to cut loose, although he has a flair for locations and situations with flamboyantly scary possibilities. The ominous Jefferson Institute might have been inspired by one of his own novels, in which antiseptic environments and sophisticated technologies are transformed into deathtraps.

The building looks forbidding from the outside -- it's actually Xerox headquarters near Lexington, Mass -- and impressively sinister on the inside, where Albert Brenner's sets and Gerald Hirschfeld's muted color photography create an abstract, dreamy setting for suspense and thrills. It's a splendidly photogenic deathtrap, and you're certainly rooting for the heroine to discover an escape route, but the escape itself is achieved too abruptly to be completely satisfying.

A scene in which Richard Widmark as the chief of surgery attempts to calm the agitated heroine may be sustained a bit too long. There's a kicker that tends to make one prematurely suspicious of him. Crichton also seems to do a bit of fast shuffling with the time sequence in the closing episode, where Douglas dashes off to prevent Bujold from ending up the next victim of irreversible coma.

Since Crichton is more inclined to err on the side of discretion, his minor bits of overdramatization are probably worth encouraging. He's almost certain to take more amusing chances in the movies he directs from now on, especially if "Coma" becomes a hit.

One of Crichton's most satisfying sequences is the climactic recognition scene in which Bujold realizes that she has made a possibly fatal error in identification just as she begins to slip into unconsciousness. It's an entertaining fusion of showdowns from Alfred Hitchcock thrillers, both of which involved Ingrid Bergman -- first in "Spellbound" and later in "Notorious." Michael Crichton has a real affinity for the psychological thriller. A little comic and romantic gusto should take him even further.