The astute new murder melodrama "Body Heat" is one of those rare movies that reinforce their themes with an insinuating, sustained tone. The first discernible image is a column of smoke from a distant fire, billowing slowly upward against a floridly tinted night sky -- the first line, heard before the speaker can be identified, is just as concise and suggestive: "My God, it's hot!" After dropping these incendiary hints, "Body Heat" proceeds to associate them with a case fo criminally destructive passion -- the hothouse atmosphere becomes a stylistic precondition for the impulse to surrender.

"Body Heat," which opens today at area theaters, could prove a memorable successor to such obvious influences as "Double Indemnity" and "Chinatown." Lawrence Kasdan, making an impressive directing debut on his own original screenplay, has borrowed the basic plot outline from "Double Indemnity." Ned Racine, a likable but corruptible young criminal lawyer played by William Hurt, pursues a halfhearted, modestly crooked practice in the small Florida town of Miranda Beach. On the prowl for casual sexual gratification, he is drawn into a torrid affair with Matty Walker (newcomer Kathleen Turner), the restless showpiece wife of a shady financier, Edmund Walker (Richard Crenna). Inevitably, the clandestine lovers nurture a plan to get rid of him. Just as inevitably, the best-laid murder plans unravel in the aftermath of the crime, but Kasdan adds some unexpected twists and fresh amoral wrinkles to the process.

While the plot descends directly from "Double Indemnity," the savory dialogue and sultry atmosphere owe a bit more to the example of Robert Towne's ominous screenplay for "Chinatown." There's no mistaking the fact that Kasdan loves the tawdry genre he's working in.

Previously overshadowed by his association as screenwriter of "The Empire Strikes Back" and "Raiders of the Lost Ark" with the spectacles of George Lucas and Steven Spielberg, Kasdan now comes into his own on the strength of an intimate, spellbinding genre film. Unlike most novice directors, he can seldom be detected groping in the dark for the right nuances and undertones. "Body Heat" seems to be the work of a seasoned, confident stylist.

As a rule, Kasdan's control is so unerring that the occasional miscalculations seem unusually disruptive. A director skillful enough to impose a style can also lull you into a false sense of security. Caught up in the unfolding narrative, you forget that everyone is subject to lapses of judgment and concentration.

For example, Kasdan overreaches for a foreshadowing symbol when he depicts Ned recoiling at the sound of a jail door clanging shut in the corridor behind him, moments after concluding a visit with an imprisoned client. The scene is not informative. It exists only to sound a symbolic clang, and as a result it rings false.

Later, Kasdan indulges an even fancier conceit, showing Ned staring at an enigmatic passerby on a Miami street -- a man in a clown costume driving a vintage red convertible. Again, the episode is superfluous and the implication trite. There's no need to call attention to the possibility that consorting with a hot number like Matty and conspiring to kill her husband may buy Big Trouble for larcenous small-timer like Ned and turn him into Passion's Fool. Their romance is calculated to look dangerous and compromising from the outset. That's what makes it hot stuff. Matty may be dressed in white when she first strides into Ned's line of sight, but she's a four-alarm vision in white.

Moreover, it's clear that sexual heat fuels the murder plot, inspiring a breakdown of inhibitions that transcends mere fornication. In this context Kasdan would probably be justified in wallowing much more graphically in sex acts than he chooses to. He prefers to make his points incisively. The affair in "Body Heat" evokes the mood one associates with the crime fiction of James M. Cain -- the mood that somehow escaped the recent remake of "The Postman Always Rings Twice," despite far more strenuous sexual groping.

Sustaining the incendiary theme, Ned devises a murder scheme that involves an act of arson. Kasdan has written several witty supporting roles and cast them expertly. One of the most engaging minor characters is Teddy Lewis, a former client, played by Mickey Rourke, whom Ned consults for advice on rigging explosive devices. It's part of Teddy's code to return a favor, but he's not happy about the sort of favor his ex-mouthpiece requires. Teddy sums up the jeopardy in his distinctive colloquial style:

"I hope you know what you're doin'. You better be pretty damn sure about it, cause if you ain't sure, don't do it. Of course, that's my recommendation anyway -- don't do it. I tell you, counselor, this arson -- this is serious crime."

Kasdan suffers a baffling lapse of directorial attention during the murder sequence. Although the story is depicted predominantly from Ned's point of view, Kasdan inexplicably loses contact with his protagonist just at the point where he must go beyond contemplating murder and actually commit murder. I'm not sure what accounts for this sudden, temporary attack of maladroitness, with the camera concentrating on the movements of Crenna while totally misplacing Hurt.

There's more involved than a bungled opportunity for suspense. Ned is the central character, and Kasdan can't do without Hurt's subtle expressive skills. In "Double Indemnity" Billy Wilder employed a narrative device that allowed the Fred MacMurray character to share his confessions with the audience. Since Kasdan doesn't resort to voice-over narration or interior monologue, the unarticulated motives must be suggested by the actors. Hurt demonstrates an uncanny ability to suggest the psychological pressures building up in Ned. He's got an impressive command of seemingly involuntary movement in his facial muscles -- little indications of tightening or slackening, particularly around the eyes and mouth -- that appears to reveal unguarded yearning, apprehension or suffering.

Given an expressive resource like Hurt, why lose sight of him during the murder? Waiting for his victim looms as an appalling moment of truth for Ned and an imaginative challenge for Hurt. Moreover, it's already been suggested that Ned may finally resolve to kill Walter because of an accidental social encounter, where he finds himself at a bizarre disadvantage with a man he happens to be cuckolding. Despite this hidden cause for sexual vanity, it's Ned who comes out of the conversation -- a brilliantly written and realized scene -- feeling emotionally exposed and humiliated.

Kasdan has composed a wonderful speech for Walker in which he implicitly brushes off Ned while outlining the philosophy that makes him a big shot: "You wouldn't believe the dorkus she was with when I met her. The guy came to us with a business proposition. We're always looking for opportunities. . . . We're willing to take an occasional risk, if the downside isn't too steep. But this guy hadn't done his homework. He didn't know the bottom line. . . . You've got to know the bottom line. That's all that really counts. . . . He was like a lot of guys you run into -- they want to get rich, they want to do it quick, they want to be there with one score. But they're not willing to do what's necessary. . ."

Ned responds, "Yea, I know that kind of guy. I can't stand that. It makes me sick."

"Me, too," says Walker.

Despite himself, Ned adds, "I'm a lot like that," and although they both start laughing, the expression around Hurt's eyes isn't funny. After this form of self-exposure, Ned may imagine that killing Walker is his only means of regaining self-respect.

While it's not difficult to account for Ned's infatuation with an apparently well-heeled mantrap like Matty, Kasdan remains suspiciously remote from her innermost feelings. Not that she's reluctant to profess her passion or demonstrate it vividly as a sexual partner. When they first meet, Maty initiates the bluntest innuendo, the once they get over the preliminaries, her appetite for Ned appears to border on the insatiable.

However, there's something suspect about her very effusiveness and avidity. The role is ingeniously written in one respect, because Matty keeps reminding Ned that she's potential poison. "You're going to be disappointed," she remarks when he tries to pick her up after an initial rebuff. Later, when Ned knows that she has deceived hom about one aspect of their scheme, she readily acknowledges that it's risky to trust her: "I'm greedy, like you said. . . I don't blame you for thinking I'm bad. I am . . . I'd understand if you just cut me off. You'd probably be smart if you never trusted me again."

It's one thing to believe that Ned can't resist her, reverse psychology and all. It's another trying to determine where we stand with her. Where does Matty's apparently genuine ardor cease and her slowly emerging deviousness begin? Since we seldom see her with anyone but Ned, the impressions are deliberately distorted by his perception of her.

Even in Kasdan's devious scheme of things it would be perferable if Matty were encountered more often in situations with other characters. I don't think there's any aspect of the character, sincere or treacherous, that Kathleen Turner couldn't embody if asked to. Her slightly tarty physical assertion and husky-voiced urgency are scarcely reassuring to begin with. She obviously means trouble, but how much trouble?

In retrospect, you understand why Kasdan feels impelled to play Matty's motives close to the vest. Still, it's a sneaky necessity that probably costs him a satisfying denouement and a certain amount of good will, particularly when movie-goers begin reflecting on the plot and discussing the twists and subterfuges with friends. Kasdan can't achieve the emotional identification with Matty that comes naturally when dealing wth Ned or the other male characters. As a result, the plot is manipulated and your head spins as you try to account for precisely what Matty must have been doing when we weren't privileged to share her sexy company.

By the time doubts arise about Kasdan's calculations, "Body Heat" has proved an absorbing, tangy entertainment. One may feel a trifle had, but there's little cause for rejection. Moreover, the virtues linger along with the nagging questions: cunning lines of dialogue; evocative settings and crisp, supple imagery; consistently sharp supporting roles and performances, notably Rourke's incisive bit as the apprehensive Teddy, Crenna's flawless embodiment of the self-satisfied Walker and Ted Danson's delightful work as Lowenstein, a convivial assistant prosecutor compelled to suspect his friend Ned in the aftermath of Walker's suden, mysterious death.

Kasdam falls short of a foolproof murder plot, and perhaps his style is too neat for a story supposedly preoccupied with overheated and overpowering impulses. Nevertheless, he's got a lot to offer the medium, beginning with an intuitive appreciation of the look and atmosphere appropriate to an effective genre thriller. The last hot attraction of the summer, "Body Heat" leaves one warmly disposed to the filmmaking aspirations of Larry Kasdan