At first psychiatrist Norman Tamarkin was "happy and flattered" when the White House called to ask him to speak on "the compulsive athletic personality."

"Then I felt a shudder of uneasiness," the Georgetown physician admitted, "about addressing this problematic side of physical activity . . .partly for a personal reason.

"When the call came, I was on a tennis court about to play an hour and a half of singles in 110-degree heat and 90 percent humidity. If I play two hours of singles, then see an open court and don't go on it and play, I feel tremendously guilty."

This type of obsessiveness, Dr. Tamarkin told several hundred health professionals at last weekend's White House Symposium on Physical Fitness and Sports Medicine, may characterize "a self-destructive phase" of athletic activity.

A compulsive athlete in this phase, he said, "uses activity the way some people use alcohol or drugs. When everything becomes secondary to physical exercise, the person may be literally running away from some deep problems."

This darker side of America's exercise explosion, Tamarkin said, is the last of three phases of intense physical activity. To illustrate each phase, he used runners as an example, "since most people who exercise regularly (nearly one of every two adult Americans say they do) are runners.

"In the first phase is the experimental or casual runner -- someone who sees everyone running and thinks he ought to do it, or who decides to run with their child, even though they haven't done physical exercise in 20 years.

"Many of these people try and quit. But those who find it pleasurable go into the second phase -- the life-enhancing phase, where most of us are. Here you see many positive changes.

"Nutrition improves as people start craving better food and less sweets, the sleeping pattern gets better, sexualilty improves, there may be decreased anxiety and people say they feel better.

"Most of these people exercise strenuously at least three or four times a week. They're serious about it."

Two problems may appear in the second phase.

"The first is what happens to a marriage or family when one member gets involved in physical activity. There are often striking changes in they dynamics of a marriage.

"Many divorces happen, not necessarily because of the running, but because running may be the straw that breaks the camel's back. A spouse might complain that the partner works 10 hours a day, then come home and runs two hours and is out on the weekends with running friends."

Tamarkin's advice for working out, this problem "is to sit down, talk about it and come up with a compromise. The best marriages are those where both spouses run. The worst seem to be when she runs and he doesn't."

The second common problem in the "self-enhancing phase" occurs if a career change or injury forces the individual to stop running. "This will result very often," said Tamarkin, "in some kind of severe blow to self-esteem.

"It means giving up an important part of life that can't be let go of easily. The person may have trouble sleeping or become anxious. Some may get more severely depressed."

When this occurs, Tamarkin suggests "talking to a physician about some alternative form of exercise -- like swimming or bicycling -- that you may be able to do without aggravating the injury.

"Try to be very careful about diet, too, since appetite may increase when activity decreases. Discipline yourself to do other things that might enhance your self-esteem -- like write letters you've been putting off because you've been using spare time for running."

Tamarkin draws the line between this second "self-enhancing" phase and the third "self-destructive" phase "when exercise begins to work against you. There's a popular book about the positive addiciton of running, but I'm talking about a negative addiction.

"These runners are the ones running two times a day, who give up their jobs, or are always late for meetings. Their families virtually get ignored. They become very dependent on exercise and become extremely anxious and feel tremendous guilt if they are not exercising.

"For example, consider an individual who runs 12 miles a day and won't eat anything but raw vegetables. He gradually loses weight and becomes weaker and weaker -- too weak to hold down a job or be a husband and a father.

"He gets injured, but doesn't listen to his body and continues his excessive exercise and diet.His wife is ready to take their child and leave, but he still won't seek treatment.

"When you're going this much overboard, you've got to look for some deep psychological problem -- usually and underlying depression. It's akin to the way some people escape with alcohol or drugs.

These people should be encouraged to seek some kind of psychological intervention."

Tamarkin, 41, classifies himself "somewhere between phase two and phase three. I haven't played tennis today, and I feel tremedously guilty. I can feel myself turning into a marshmallow mess."