Dianne Durham and Mary Lou Retton were indistinguishable from the other kids trick-or-treating in the northwestern part of Houston last month. At 15, they were a trifle old perhaps, but no one took particular notice of the blue-and-pink-haired punk rocker or the black-caped witch as they went from house to house. Come next summer, however, Retton and Durham may find themselves in every house in the land—not as trick-or-treaters but as Olympic gymnasts, either one of whom could become the first American female to win a gymnastics medal in more than 35 years.

Durham, the bewitching one, and Retton, of the blue-and-pink hair, are both training with Bela Karolyi, the Rumanian coach who introduced Nadia Comaneci to the world seven years ago. Bela defected to the U.S. in 1981, and now runs Karolyi's World Gymnastics, Inc. in Houston. The academy has 300 students, but there is no question about who are Karolyi's most prized pupils. "The Little One [Retton] is simply great," says Karolyi, in his Transylvanian accent, while "Dianne has speed, natural body strength, dedication and self-confidence." Durham is the top-ranked gymnast in the country, and Retton is tied for No. 3 (with Pam Bileck). These three, along with Julianne McNamara (No. 2), Kathy Johnson and Tracee Talavera, represent America's best hopes for a medal.

Durham and Retton provide a striking contrast to Comaneci. Where Nadia was sinewy but slight, the Americans are strong-limbed, with muscular thighs and broad shoulders. The contrast is emotional as well. "These kids aren't as calculating as Nadia," says Karolyi. "They are more like gamblers, throwing themselves totally into a competition."

The 4'9", 92-pound Retton is a dynamo in competition (which includes floor exercises as well as the uneven bars, balance beam and vaulting horse). In her best routine, Mary Lou handsprings over the horse, then, uncorked, twists twice in the air before landing. Taller but equally lithe at 5'1" and 105 pounds, Durham practically detonates during floor exercises, her best event. Springing into the air, she completes two backward somersaults, her legs straight, while twirling in midair.

Understandably, a certain rivalry has developed between the teenagers. As Olympic women's coach Don Peters observes, "They spur each other on." The gymnasts agree that their toe-to-toe, day-to-day, seven-day-a-week training regimen has strengthened them. "We are good friends," says Retton, "but there is a feeling that if she can do it, I can do it. If she does well, then I have to do well too."

Spring will bring two crucial tests. In May they will compete in the U.S. championships, and the Olympic Trials will be held the following month. A squad of seven will be chosen to face, among others, the Russians in Los Angeles. The Soviets are counting on the likes of Olga Bicherova, 17, or Natalia Yurchenko, 18.

Retton vaulted into prominence last March when she took top honors at the McDonald's American Cup competition. Retton, who began gymnastics at 7, was lucky to be competing at all; as an alternate she was subbing on one day's notice for an injured Durham. Mary Lou comes from Fairmont, W.Va., but she is boarding with a Houston family while training with Karolyi. She attends school via correspondence course and admits to occasional bouts of homesickness for West Virginia, where her father owns a coal-mining equipment company. "I get a little weepy sometimes," she confesses, "but I want to reach my peak. There will be time for other things later."

Durham too was homesick, so her mother moved to Houston temporarily. The $20,000 annual cost of keeping Dianne in leotards and studying with a tutor has strained the family budget, her mother says. Dianne, who began gymnastics at 4 when her father, the director of industrial relations at a steel mill in Gary, Ind., spotted a course ad, had a self-described case of burnout at 12, quitting for 18 months.

Now committed once again, Durham is concentrating on Los Angeles. Although she would be the first black ever to win a medal in gymnastics, Durham says, "I never even give the black part a thought. But," she adds, "winning the Gold...Oh, wow."