SWIMMING CAREERS, even by today's standards, are generally meteoric. Stars flash to the top, take the swimming world by storm and disappear as quickly as they appeared.

Don Schollander was unbeatable in 1964 but human in 1968, Mark Spitz failed in 1968 before his triumph in 1972. Remember Rick DeMont? Untouchable in 1972, he failed to make the Olympic team in 1976.

And these are three swimmers who stayed near the top longer than most. Melissa Belote came from relative obscurity to win three gold medals in Munich Olympics in 1972. She was 15 at the time.

Four years later she returned to the Olympic, but this time there were no medals. She swam in one event - the 200-meter backstroke, and finished fifth. She was disappointed. A year later she is still swimming; she says it doesn't hurt quite so much now. "I try to put things in perspective," she said last week on the morning she was scheduled to return to Arizona State University. "I was disappointed at first when I didn't win anything; I guess I said nasty things to myself about the East Germans and all. But I got over it. You always do.

"Now I look at it differently. I swam my best time; I was the only American in the final; I did the best I could. When I look back at Montreal now I feel very happy about what I did."

The 20-year-old college junior of 1977 is very different from the 15-year-old girl of 1972. Sitting in her parents' Springfield home wearing a white blouse and blue slacks, discussing school and her summer, Belote could be just another college girl.

But the living room effects give her away. Over the piano is a picture of her in an Olympic bathing suit; tucked in the corner of the room is a bookcase filled to overflowing with trophies, medals and awards. In the cellar sit 22 boxes filled with awards.

But while Belote does not shrug off her accomplishments and remembers Munich fondly, she admits her attitude towards swimming has changed.

"I still love to work out," she aaid, shaking her head in wonder that she still could frame such a thought. "I don't know why, maybe I'm a masochist or something, but I've always liked workouts better than meets.

"At this point I have to look for new challenges to keep me going and I can get them in practice. Forcing yourself to push through your pain barrier is the biggest challenge any swimmer faces. I'm glad I can still do it.

"But it isn't the same as before. How could it be? When I was 15 swimming was IT for me. Now I have a social life. If I couldn't have it because of swimming I would quit swimming. I need other things now besides swmimming."

Why go on? Belote has won everything there is to win. She had been in two Olympics, a rarity for a swimmer. Her swimming scholarship at Arizona State does not require her to work as hard as she does.

"I still like it and as long as it's still fun I'll keep doing it," she said. "Of course I've thought of quitting, thousand of times. I've come home after a bad workout and sworn I'd never go back to that pool. But I go back.

"I know it can't go on forever. But when I'm out of swimming I know I'm going to want to stay involved in it some way.

It had been a long summer for Belote. She changed her major to mass communication and had to take a summer course at Maryland University in news reporting. She worked out every morning at the Cardinal Hill swimming pool. In the afternoons she helped out at workouts for the age-group team at Cardinal Hill.

Despite that "light" workout schedules, she still qualified for the U.S. team that traveled to East Germnay and the Soviet Union Aug. 20-Sept. 6. She admits that travelling is one of the things that keeps her going.

"Actually, I'm really happy with the way I swam this summer considering all the other things I was doing," she said. "I've got about a three-week break now and then it's back into the water."

When she dives back in, Belote will have several decisions to make. One will be whether to try to qualify for the World Games next summer. And in the back of her mind is a third Olympics. No American woman has ever swum in three Olympics.

"It will comes down to mental attitude," Belote said, a somber look flashing across her face for the first time. "If I still have the dedication and the desire I might try for it. I'll graduate in 1979 and I might decide I want to try it again.

"But I don't know if I'll have the incentive to work that hard. Other things may come first. I turned down the Pan American games in 1975 because it would mean missing a month of school."

Her parents, Florence and Buddy Belote, say they'll support any decision she makes. If she wants another shot at the Olympics she can train here with longtime coach Ed Solotar or at ASU with Ron Johnson.

"I'm not even worried about it," her mother said. "Melissa's always been mature about her decisions. People can never believe she's the way she is. When she answers the phone sometimes people won't believe it's her. They can't believe she would answer her own phone.

The limelight has never bothered Belote. She is articulate and able to handle people; she has grown into an attractive woman with hazel-gray eyes that sparkle in the sunlight and short blonde hair.

She could retire tomorrow, her place in swimming history assured. And, like many swimmers who have been at it for a long time, she admits to mixed feelings about the end. The pain will not be missed but the sport will.

"People keep asking me when am I going to retire," she said, laughing. "I think about it more and more now. I've been swimming different events at schools to try and find something else to do. My backstroke hasn't improved that much since 1972 and won't improve much more , either.

"Workouts can be upsetting. I'm a perfectionist and I don't like not doing well. I get angry. But as I've gotten older I've realized that you're going to lose races and you're going to hit plateaus."

Belote isn't sure whether she's reached that final plateau. She admits that swimming "is not my No. 1 priority anymore."

She did not, and will not, criticize the muscular East German women who surpassed her world records at Montreal. But she predicts "American women will be back. They're already on the way."

Whether Belote will be with them in Moscow at age 23 is another matter. As swimmers age - and 20 is ancient - the discipline becomes harder to accept.

"If I decide to try for '80 I really believe I'll make it," she said. "I'll make it because I know what you need to do, I know what kind of dedication it takes.

"But if I decide not to try, I'll be happy with that decision too. There will be other things to do. I won't have any regrets."