The plot line of ABC's Sunday night movie this week, The Making of a Male Model, centers on a steamy linkage that seems simple and gamy enough: A strapping, on-the-make hunk tries to make it to the top of the New York modeling business, aided by an older sexual piranha who as an agency head has lured him to the big city from Nevada. The casting might have seemed a natural: Jon-Erik Hexum, 25, plays the beefcake (Jon-Erik Who?). As for the powerful seductress, suffice it to say the producers landed a big one: Dynasty's Royal Wryness, Joan Collins. Hexum, about half Collins' age, pulled down half her $100,000 fee; offscreen, though, they've both been seen around L.A. enough to tease tabloids and fuel gossip of a real-life fling.

Predictably, the denials are vague and tantalizing. Says Hexum, a native of Tenafly, N.J., "It's not a romance. But it's not that it would never be." Collins needs fewer negatives. "We're just friends," she says. Of course, this is the same Collins who dismissed as "rubbish" the rumors of her impending split from Ron Kass only days before they separated nine months ago after 10 years of marriage.

Who would blame Joanie, even if the attraction were purely physical? Certainly not Jon-Erik. "Some people," he admits, "are insecure around me because of my looks." But he's a sensitive guy. "I try to make them feel less insecure by paying attention to them and what they are interested in."

It's not at all like that in the TV movie, the theme of which seems just a tad short of novel. "The movie's about the materialism of the modeling industry," he explains, "where you have nothing but a look." Amen.

Yet Hexum, a 6'1", 190-pound Michigan State University football receiver, diver and wrestler, with a 1980 B.A. in social science, knew his own pretty face was marketable. After college he hurled himself into "an endless parade" for Manhattan modeling and acting agents. He worked odd jobs at night to pay for rent and acting lessons. His break may be a Hollywood first: He was a free-lance housecleaner, and one place he did belonged to a friend of John Travolta's former manager, Bob Le Mond. "I guess the guy saw a lot of talent in the way I cleaned Venetian blinds," he cracks. Soon Hexum could unplug his Hoover, and Le Mond was polishing up his new client for stardom.

After only four months in L.A., Hexum hit $10,000-a-week paydirt as Phineas Bogg, a time traveler in an ambitious NBC bomb, The Voyagers! Unfortunately, the series was slotted opposite 60 Minutes. After 22 episodes, the show went belly-up.

Not Hexum. The younger of two sons of Norwegian parents who divorced when he was 4 (he hasn't seen his chef dad in 16 years), he debuted onstage in second grade. Recalls his mother, Gretha, now 60 and a career aide who lives in a townhouse he bought her north of L.A., "His teacher back then said she never had a student with so much determination."

He remains that way professionally—taking weekly lessons for voice, acting and dance. Romantically, however, it's another story. Somehow Hexum has been hexed in love. As for ladies, he protests, "I have no way to meet them. I'm alone when I go to bed at night." The likable Hexum even has an answer to one plausible theory about his lack of female companionship. "Gay, I ain't," he blurts out, adding, "I don't want to be thought of as gay, although 80 percent of my friends are."

Whatever social contacts he maintains, he says, "My friends think it's ridiculous the way I live." In a word: minimalist. His latest place is a three-bedroom bunker in Burbank so close to the airport he has to stop talking on phones during takeoffs and landings. Furnishings are Spartan—a piano, some packed cartons, a mattress on the floor. If he often eats burgers behind the wheel of his funky '54 Chevy two-tone, it may be because "I borrowed myself into oblivion" while in college. "I'll be paying loans off until 1997."

Maybe not. He decided not to try for the role of Collins' young stud on Dynasty. That three-year commitment might have stood in the way of an even bigger movie break. Hexum is said to be director Hal Needham's choice for Terry and the Pirates, a film in the works of the famed comic strip. He's modeled suits for Valentino and jackets for Versace, and he's got a topless, look-at-those-pecs poster in circulation. At least one female was not knocked out by the pose: "I don't like it very much," sniffs co-star Collins. "To be honest, I'm not an armpit person." Hexum has obviously spent enough time around fast-tongued Collins—on or off camera—to come up with the perfect retort. "I'm commercial as hell as a hunk."