Swimming is the ascendant star in the cosmos of physical fitness. Pools everywhere are filling with pilgrims of the whole-body grail, many of whom have turned from more traumatic sports to stroke toward better selves.

Endurance swimming has nothing to do with splashing about in the shallows. This is water work, one lap accumulated upon another to a mile or more of continuous strokes and kicks, steady movements of the body in an environment of restricted sight and sound where the tactile sensations are so uniform that they soon become muted reflections of the skin.

The morning breath of chlorine. Greenish aquarium light, the tiled line rippling beneath your belly, bobbing lane floats, the wall you touch as you turn. Splashes blending into a froth of sound, your exhaled breath gurgling out across your chin. A long sinuous line of muscular effort from the palm of your hand to the face of your foot.

Each swimming movement is more costly than its airborne twin, but in water the effort is unrestricted. No ground crashes against foot and knee; no sudden shift tricks and twists vulnerable connections of bone and cartilage and ligament. As its owner swims, the human back is freed from upright compression. Swimming feels good. Any kid knows that much, and now more and more adults have decided to recapture the feeling.

"Running exploded 10 years ago," says Dr. David Johnson, former national 200-meter medley champion and member of the 1968 U.S. Olympic swimming team. "Now the same thing is happening with swimming."

Johnson, an instructor in clinical orthopedics at Georgetown University Hospital, says one reason for the increase in numbers of swimmers is that his profession is sending the wounded from running and other sports to the pool for therapy.

"When you swim, you're using more muscles than in any other sport except cross-country skiing, and using them in a gentle fashion. It's a safe form of exercise that maximizes muscle use while minimizing the chance of injury," he says.

While Johnson was still in swimming competition, his resting pulse rate, a common indicator of heart and body condition, was 38 beats a minute. Now, at age 35, no longer working out daily at the pool, his resting rate is still only 42, a little more than half the average of the general population.

And, Johnson says, he can go on swimming as he gets older, longer than with any other endurance exercise.

Serious swimmers find the sport as therapeutic for the head as for the body. Harvey Wiener, author of Total Swimming, says:

"The swimmer's high is stronger, completer, richer in its capacity for release and relaxation, longer lasting and more devoid of connections with pain than the elevated feeling that accompanies other sports."

Whatever the physiological, metaphysical or just sensual attractions, more people are methodically swimming now than before.

Benny McCottry of the D.C. aquatics program says the District's pools have "seen a tremendous pickup in lap swimming in the last couple of years." Other public and private pool managers report the same thing.

Moving through water, a body acquires its own natural sense of form and grace. Swimming's smooth unsyncopated rhythm returns a childlike sense of freedom. And when the workout is over, the swimmer's body feels loose and unstressed, a child again, going home from an afternoon of shoeless play.