What figment is this of Hollywood past, descended in character from the movie screen to pace her hotel room like a genie tricked back into the bottle? The couch, the rug, the other demonstrable realities exclude her. Against them she seems almost transparent, a phantasm in a white linen dress set glowing by the window's glare.

Her name is Kathleen Turner.

Her eyes are wide, her face open. Blond hair spills down her neck like the American side of Niagara Falls. She is remote, perhaps vulnerable. Or perhaps not. It is cool in the room. But in "Body Heat," her first film, it is sweltering, and her character, Matty Walker, does everything to raise the temperature further.

"I don't think of myself as a sex bomb," she says thoughtfully. "It was fun to explore that in Matty. But it's not my self-image."

"Body Heat" is already being hailed as a grand achievement of romance and passion -- a modern "Double Indemnity," the movie the latest "The Postman Always Rings Twice" tried to be but wasn't; a torrid, sizzling, scarifyingly passionate tale of a love affair too hot not to put somebody on ice.

Matty is the mysterious beauty unaccountably alone at the bar. Into this dangerous space slips William Hurt, as Ned Racine, a good-natured, good-looking, slightly corrupt local attorney. As the languorous heat, the sensual motive, and the suggested opportunity combine to draw Ned inexorably toward his carefully scripted fate, Matty smiles and says fondly:

"You're not too smart, are you? I like that in a man."

She has a husband, but he's "small, and mean and weak." He's also rich.And out of town. Under the spell of the wind chimes of her ocean-front mansion they fall in love. It is very hot, and their bodies glisten. Matty explains: "My temperature always runs a little over normal."

That is not all that runs a little over normal. The husband disappears. The police appear. And with growing panic, Ned Racine begins to remember through the sensual haze what it was she liked about a man . . .

But this is a hotel room, not a movie set, this is reality, not illusion, this is a cool August morning, not a Florida heat wave in the film noir style, and this is Kathleen Turner, not Matty Walker.

"I believe Matty is capable of love," she says. "It's just that she doesn't let that stand in her way."

This comment is thoroughly in character. Which character, only the illusion knows. But here we have the figment of imagination, standing for examination. Strange, for in this very hotel, in recent years, actresses on tour have hastened to destroy their movie characters in favor of the Truth About Themselves. At pains they have pointed out, in faded jeans, the point where their roles and their selves part. They have talked about foreign policy and rock 'n' roll, and presidential candidates, trashing the illusion. Never mind the movie, ask me what I think of nuclear power. Life was a talk show, and their feet hurt, and they talked about it. But that was then, and this is now.

Turner rises, pacing. Or is it Walker? She tosses her head, the hair flying; turns; stops; says with intensity, almost accusation:

"There was a scene that we shot that was cut out.Because it wasn't needed, it would have been overstatement. Because the audience would know about Matty through the foreshadowing, the hints of what is to come."

She advances, her lip quivering unaccountably.

"Why haven't you called me?" she says.

Her guest looks behind him, startled. There is no one else in the room. It is suddenly very warm, as warm as Florida in August.

"Why haven't you called me?" she says, slipping off a phantom blouse. "Is anything wrong?" Slipping off a phantom belt. "Ned? tell me, please." The lip quivering still, as the pantomined skirt slips to the floor. She has come very close, gazing with the eyes of a wrongly punished child.

Seeing heads of perspiration appear on her guest's forehead, and all other life signs suddenly gone, she leans back with an enigmatic smile.

"But that scene wasn't necessary, so it was cut," Kathleen Turner says, her Matty voice dissolving only a little, for in fact it is not so different from her Kathleen voice. "This is a sophisticated film, more than some others. And that was just about the only cut, because Larry is really brilliant, and he wrote the screenplay himself and hardly a word was changed."

Larry is Lawrence Kasdan, the screenwriter of "The Empire Strikes Back" and "Riaders of the Lost Ark," who wrote "Body Heat" and directed it as well. Turner was 25 when she appeared in his office to read for the part of Matty. Her most notable credit was 18 months as Nola Aldrich, a bad beauty on the soap opera "The Doctors."

"Larry handed me the scene where Matty talks about her past. I just stretched out on the couch and did it, and when I finished, he said, I didn't think I'd ever hear the part read exactly as I wrote it.'"

Kasdan, who read 150 other women for the part, stopped when he heard that voice. ("She doesn't fit into a niche with anybody," Kasdan is officially quoted. ". . . An absolutely magnificent vocal quality. . . . She's going to fill a spot in our female stars category that sorely needs filling.")

Indeed, it is a voice to make Lauren Bacall turn her head -- and whisk Humphrey Bogart out of the room. It is a voice so chesty and remarkable that each word, forming within, seems to linger a moment in fond farewell before its reluctant emigration from the mouth. When she arrived in New York, after graduating from the University of Maryland in Baltimore, her first agent told her that unusual voice would have to go. But it was the agent who went.

She believes there is something about "Body Heat" that sets it apart from other films.

"It's the dialogue, the words. You want to listen, you need to follow it. I think its so important that the movies are getting good writers now. David Mamet's "Postman." John Guare, who did "Atlantic City." And it's important that Larry has not assessed the value of these characters. Is Matty this? Or that? You never really know."

And Kathleen -- is she this? Or is she that? Ah, but the illusion shields her like a gauze. Formerly unfashionable, but now suggesting another time and another Turner, Lana -- a time when stars remained in costume off their sets, and when Hollywood knew its own role and played it as skillfully as its actors.

One thing she is; the daughter of a foreign-service officer. She lived in Canada, and Cuba, and when her father was posted to Washington she lived in Bethesda and went to second and third grades at the Westbrook School. Then Caracas, Venezuela, and London. Where, at the Central School of Speech and Drama she studied acting. When her father died, she found herself transported to Missouri, where her mother's family lived, and enrolled at Southwest Missouri State University.

"The cultural shock was the worst imaginable," she explained. "My hair was quite short, but the other girls' was long. All of my skirts were midis, but they were all in minis. That cast doubts on my sexuality, I think. I didn't help the adjustment much. On my first date, the boy asked me how I liked school. I remember saying, with full English accent, "Oh the school's all right, but the people are so bloody stupid . I was quite affected, I'm sure. But I was just drawing on a different pool of experience, from living abroad. When the kids talked about 'Leave It to Beaver,' I didn't even know what it was."

As soon as she could she transferred to Maryland, and earned a MFA degree, and won her first professional role -- as aningenue in the Maryland Bicentennial Pageant that played the Merriweather Post Pavilion. In New York, she worked on the soap by day and in the cast of the Broadway show "Gemini" for nine months. She had been in Canada in a production of Chekhov's "The Seagull" when the chance to read for "Body Heat" came.

The sosp was her training ground, she says. On the small set, crowded round with three cameras, reading lines for a TelePrompTer, the melodrama chrning out, she "learned to handle a camera."

"Oh, I loved it. I found out that you could do things just with the rate at which you open and close your eyes. Things that in a theater would be lost except to the first 10 rows. And things with your voice, that you could never do on stage." She was unitimidated when the heavy gray cameras rolled close up, within three feet, implacable, revealing.

In many of her scenes in "Body Heat," she and William Hurt are in varied stages of undress. They are falling in love, and then they are in love, and then they are falling into murder. They perspire. In fact, the movie seems to glisten passionately from beginning to end. What everyone wants to know: what Bill Hurt is really like, up that close?

"All that sweating was accomplished with spritzer bottlers," she explains. "They sprayted us down. The scenes on the beach wre shot in December, so it was actually very cold." But she does not continue, careful of the illusion.

"And Bill was wonderful. He'd had a lot of those kinds of scenes with Blair Brown in "Altered States," and that was a help. We went to see "Altered States" together during the filming. You remember? The posters showed him dangling upside down. So we all walked past the theater in Los Angeles, bent over with our heads upside down."

Turner lives in New York. Sometimes she goes bowling at 11 o'clock at night with her friends at a 10-lane Manhattan alley. Her best score is 175. She stays up late. When it is necessary, she gets up early. She draws on the pool of experience from her childhood abroad, and adds to it from the experiences of her adulthood here.She would like to do "Uncle Vanya" next, with Lloyd Richards at the Yale School of Drama.

She is quite beautiful, which is not unusual, and somewhat mysterious, which is. She says she has not completed her "film education," whichmeans she hasn't seen "Double Indemnity." Of her long-running soap opera character she says only one disparaging thing: "Nola was an imcompetent villainess."

They are saying she is "one the threshold of stardom." That has always been a crowded threshold, and the room beyond vast and nearly empty. But if the 1980s return to romance and illusion, she may find herself already there.

"I don't feel any pressure to follow this up," Turner said in that remarkable voice. "I've got 50 years left in this business. I'm told you're known as much for what you won't do as for what you will."