A Change of Sport, Change of Habit : Olympic Festival: Mills trades in her gymnastics leotard for the swimsuit of a diver, but she trains differently.

Once the star of all Bela Karolyi’s gymnasts, Phoebe Mills knows the meaning of burnout. She doesn’t intend to make the same mistake twice.

Mills, 20, will compete on the platform and three-meter board in the diving competition, which begins today at the U.S. Olympic Festival.

She turned to diving four years ago, after retiring from gymnastics. Although she was known for her intensity in gymnastics, her approach toward diving is much more relaxed. This time, she’s in it strictly for fun.

“Diving is a little bit more laid back for me,” Mills said. “I really just want to keep improving and enjoy myself.”

The months after she won the bronze medal at the 1988 Olympics should have been filled with celebration for Mills. Instead, at 15, she was exhausted.

Even after two weeks of rest, and after returning to Karolyi’s gym at Houston to resume training, she could not shake a sore throat that she picked up at the Olympics. The condition was diagnosed as the Epstein-Barr virus, which also is often associated with chronic fatigue.

What’s more, thoughts of a life that did not involve eight hours of practice every day increasingly enticed Mills.

She called her mother, Susan, in Winnetka, Ill.

“Please come pick me up,” Mills said.

The decision to leave gymnastics was monumental. Not only did Karolyi have hopes for Mills to continue in gymnastics, but also, she had grown accustomed to the structure of training.

“It was a big decision because (gymnastics) had taken up so much of my life,” Mills said. “All I had done was just train, so I was kind of lost because I didn’t have that base I had for so many years. Ultimately, I knew I had to make the decision myself. I’m glad the way it turned out.”

Mills began diving as a junior at New Trier High in Winnetka. The next year, she moved to Boca Raton, Fla., for more serious training.

But this time around, Mills knew her limits. She trains half as much as she did in gymnastics.

“I just need to be aware of it,” Mills said. “A lot of times, I don’t want to take the time to sleep a little longer, but I have to.”

This is Mills’ second time competing in the festival. As a gymnast, she won a silver medal in the all-around in 1986. She shares the women’s record for the most medals at a single festival with six.

Then, Mills was one of the nation’s brightest Olympic hopefuls. This time, she would have to improve considerably to make a return trip to the Olympics.

Mills placed 13th on the platform at the national diving championships at Austin, Tex., in April. At the U.S. Olympic trials in 1996, only the top two divers in each event will make the team.

But Mills cannot be counted out.

“She always is going to be setting goals,” Susan Mills said. “She’s just that kind of a person.”

As a gymnast, she was known as a perfectionist.

Karolyi, who has trained some of the world’s most famous gymnasts, including Nadia Comaneci and Mary Lou Retton, said that Mills’ work ethic was excellent.

“She was a quiet little girl with a tremendous desire to come up to the Olympic level,” Karolyi said. “She was a beautiful page in my long coaching career.”

But that page is turned. Mills looks back on her time with Karolyi fondly and says she has no regrets about not continuing in gymnastics because she accomplished everything she wanted.

She has grown 2 1/2 inches and gained 17 pounds--to 5-1 1/2, 105--since the 1988 Olympics.

She has done well in her new sport because diving is so similar to gymnastics. The main difference is that you land headfirst in water, instead of feet first on land.

“It takes a while to get used to,” Mills said.

But there are other differences. Mills had to learn how to compensate for the spring on the one- and three-meter boards.

She has no trouble with the tricks in the air. The most difficult thing about diving, however, is making a clean entry into the water. That can be gained only through experience.

Mills has a long way to go before she reaches the same level in diving that she reached in gymnastics.

“It is frustrating sometimes,” she said. “It’s a long road to get to the top of anything you’re doing.”

Then she smiled. On this road, she will be taking her time along the way.