TOM CRUISE, the enterprising hero of "Risky Business," never went to college and never took an acting lesson. One tells him he's "a natural" and he says cheerfully, "That's just the word for it." One tells him he's a star, at 21 yet, and he says, "Yeah. It's too much. Sometimes I ask myself, 'Why me?' "

And if one told him that the grosses on "Risky Business" total just over $28 million as of this past weekend, he would probably say he wished he had a percentage of the take, which he doesn't. Yet his asking price per film has shot up into big leagues (just how big, his agent doesn't want to say) and he's been able to rise rapidly to the top of the current Young Actor Crop without stooping to anything really dumb or self-demeaning on the screen.

In "Risky Business," as a matter of fact, he and writer-director Paul Brickman utterly revitalize the screen image of the young man who undergoes movie-dreamy sexual initiation. They made it movier and dreamier than ever, yet the film is also caustically funny. Cruise plays Joel Goodsen, a 17-year-old suburban Chicagoan whose parents leave him alone in their WASP-elegant home while they go off on vacation, wherein lies the tale.

Joel's first taste of freedom is rather hesitant; he turns up the stereo to blast range and eats TV dinners without unfreezing them. But he grows in the role, calls a call girl for a long night's night, and, eventually, turns his parents' home into the best little funhouse in Glencoe. The picture is a sensational writing-directing debut for Brickman, one that caught even executives at Warner Bros. by surprise (and went right over the heads of some movie critics), but it is also Cruise's golden moment.

He is ingenuous and vulnerable on the screen in ways that audiences find terribly attractive, but unlike some of the other young actors around these days, there's nothing of the neurotic wimp about him. In person, Cruise is solemn and sober; his blue-gray eyes lock into high seriousness when he discusses his "craft" and how dedicated he is to it. He doesn't want to contemplate his status as a sex object, but his manicured composure crinkles a little, and he allows himself a broad smile, when told that, at a recent showing of the film in Westwood (L.A.'s Georgetown), after a scene in which Cruise dances in his underpants to a Bob Seger rock tune, a young woman in the audience shouted, "Encore!"

In the Los Angeles Times last week, another young lady was quoted saying of Cruise, "He's such a babe"--perhaps just what the New Everyman would like said of him by the New Everywoman--and People magazine has officially dubbed him a "teen heartthrob" in a current story, though thankfully the magazine seems to have retired the term "hunk," at least for one week.

"It doesn't matter to me," says Cruise of such talk. "I focus on my craft, my work. That is the most important thing to me. And what people say, if I let it bother me, I'm going to be in a lot of trouble. I just focus in on what I want and what I want to do, and everything outside of that is just there, and it happens. Whatever."

His visage will not be seen grinning toothfully from the cover of Tiger Beat magazine and that ilk, Cruise says; nor is he likely to make an embarrassing public spectacle of himself.

"You won't see that, no, because I have a certain amount of control over that. I'm getting young audiences in to see my films without doing that kind of thing," Cruise says. "And I'm not locking myself into a teen idol stereotype. I mean, I'm free; I can do anything. I have to make transitions in my life. I'm growing, and I'm going to work into older roles."

Cruise made a strong impression in his first major film role, the trigger-happy cadet of "Taps"--indeed, such a strong impression that the part was beefed up for him during filming. "The character's so intense, it took me months just to come down from the role," Cruise says. "I mean, after the film, I had no sense of humor whatsoever." This isn't hard to believe.

He spent some time on the set with George C. Scott, the ultimate grizzled old pro, who was briefly in the film. "He told us a lot of stories about when he was growing up. You know, when he was an actor. He used to play chess for money and sell a pint of his blood for cash and use half of it to bet on chess and the other half of it to drink. Argggh! The good old days."

Cruise also had a tiny part in Franco Zeffirelli's morbidly mushy "Endless Love": "I was the kid who came off the soccer field and gave the guy the idea to burn down the house." He didn't like the finished film. "For my tastes, it was overly hot." Then he went to work for another illustrious Italian, Francis Ford Coppola, on the semi-successful film version of "The Outsiders."

Coppola he found to be "just like one of the guys. And he totally trusted me. He let me go anywhere I wanted to go with the character. And he even upgraded the character. He kept trying to find more for me to do. He was very encouraging--just like, 'Hey, Francis.' He'd eat with us. He'd cook for us." Cook what? "Pasta, of course."

Cruise auditioned for the part of Joel Goodsen while working on "The Outsiders." He flew overnight from the Oklahoma location to Los Angeles for the test, staying in costume so as not to lose his grip on the blue-collar punk he was playing in the film. "I was like filthy, dirty, stunk, and my hair's all greasy, and I had a tattoo on and I had this chipped tooth for the role. And here I am, just explaining to Paul Brickman which way I'm going to go with the character in terms of losing the weight and what I would wear. So it's pretty amazing that they cast me in the role."

Somewhere in there, Cruise made another picture, called "Tijuana," which he describes as "not a very good one" and which got shelved by Embassy Pictures after a brief release. It may turn up on cable TV some day. "It doesn't matter to me," Cruise says coldly. Meanwhile, he decided he had to lose precisely 12 pounds to play Joel Goodsen. And did.

The hardest scene to shoot in "Risky Business" was the love scene, with costar Rebecca De Mornay, aboard the moving Chicago commuter train, one of the more blissfully erotic sequences in recent American filmdom. "It was hard to shoot because we were shooting it in Chicago and we had 15 minutes on the track and we had to get off for 15 minutes because trains were passing by. From like 10 at night to 6 in the morning," Cruise recalls.

But he agreed it was pretty sexy stuff when he saw it all put together. "I was very proud of it. It's such an incredible job. Paul worked on that scene for about a week, just editing it. He kept telling me, 'Wait till you see the love scene; it's going to blow you out of the water.' I said, 'All right!' I sat down in the screening room and he kept hitting me and looking at me while I watched it.

"But the hardest scene for him to edit was the dance scene, in the living room in the underwear . Most of that was ad lib. Yeah. All of that was ad lib. And so I wasn't matching things. So I was getting a call from him every day cursing me out."

The last scene in the film, a slightly ironic kicker that sends Joel out of our lives on a note of triumph, wasn't there in the original cut of the picture. It originally ended, Cruise says, with Joel and the hooker going their separate ways, a more downbeat fade-out. But preview audiences liked Joel, and they wanted to see him win out. They wanted his experiment in private enterprise to bring him a reward. They wanted him, if not to get the girl the way Dustin Hoffman did in "The Graduate," at least to get into Princeton.

"Personally," says Cruise, he liked the downbeat ending better, but agrees the other one is "more commercial." So he learned a little lesson about capitalism the way Joel learned a little lesson about capitalism. Sort of.

Cruise doesn't have particularly vivid memories of his own high school life. His parents divorced when he was 11, and the family moved around a lot, so he went to three different high schools, and had few friends, he says. He has trouble thinking of the craziest thing he ever did in high school, a time, traditionally, of crazy things.

"Oh, I don't know. Let's see--one of the crazy things, I put the school up for sale. Got, you know, one of those signs, 'For Sale,' and put it up in front. You know, ha ha." He realizes this isn't very crazy. "In Kentucky, when I was a freshman, my best friend and I used to sneak the car out at night, and I wrecked it. I wrecked the car! In the middle of the night, I wrecked it!" In the film, Joel Goodsen accidentally sinks his father's $40,000 Porsche in Lake Michigan.

"I was going the wrong way on a one-way street when I bashed the door up," Cruise continues. "I was very short at the time, and I had a hard time seeing over the dashboard. This cop pulls us over and says, 'You know, you're going the wrong way on a one-way street.' I said, 'Thank you, officer, I appreciate that. I will turn around.' And so my friend Jeff gets out of the car and I still had to back it up, so he jumped out of the way, but there was a parking meter there, and he got caught between the door and the parking meter by his crotch. He's screaming 'Help! Help!'

"Anyway, we did this every night throughout the summer. We'd take the car out and we'd say, 'Oh yeah, we're going to pick up some girls.' I mean, what girls are out at 4 and 5 o'clock in the morning?" Was he drunk? "No," Cruise says. "Just naturally crazed."

Later, after he had moved to New Jersey and a wrestling injury put the kibosh on his high school athletic career, Cruise got a part in a student production of "Guys and Dolls," specifically, the part of Gold Old Reliable Nathan, Nathan Nathan Nathan Detroit. And he was so taken with the idea of acting that he left home at the age of 18 and has been working steadily, more or less, ever since. He rents an apartment in fashionable Brentwood, but is fashionably almost never there.

His next film, already completed, has Cruise cast as a factory worker of Yugoslavian background in "All the Right Moves," shot in Johnstown, Pa. It opens in a few theaters on Sept. 23, then in more theaters in October. And Cruise is involved in another movie project with his friend Emilio Estevez, son of actor Martin Sheen. Sheen is playing John F. Kennedy in a TV movie to be seen this season, and so Cruise went over to the set and looked at footage of the Kennedy assassination. "That stuff is just in-tense," he says. He was 1 year old in 1963.

He doesn't mind being called a kid, and even named his production company Kid Cruise Productions just to prove it; when actors start making a lot of money, they form production companies, almost as a reflex action. Cruise says he has been offered parts in teen-cretin films--the leering, yahoo things like "Porky's"--but won't take them. "I'm very careful," he says, "now that I have somewhat of a following, not to bring my audience into a film that's going to exploit women and make young people look like idiots and just a bunch of sex fiends. You know, why do that?"

As a demonstration of his seriousness, he says he would like to meet Laurence Olivier. What would he say to the good lord? Cruise lets his sobriety dissolve, brightens into a huge grin and says loudly, "Hey dude, what's happening?," bursting into laughter--you know, ha ha. And Kid Cruise is a kid again, if only for a second.