Every morning at 4:30 John Rush hangs himself. Upside down. From the ceiling of his Arlington apartment.

"It feels fantastic," says the 30-year-old Agriculture Department employe and part-time model who dangles, batlike, two or three times a day: in the morning, after work and before bed.

"It's a great way to wake up, to meditate, to exercise or to stretch out after a long day on your feet."

Rush hangs with the aid of "gravity/inversion" equipment -- familiar to those who saw actor Richard Gere lift weights while hanging upside down in the movie "American Gigolo."

The minute he rolls out of his inflatable "air bed" at 4:30 a.m. ("i grew up on a farm, and I like leisurely mornings"), Rush snaps on metal and foam "inversion boots." He grabs a steel bar on his "gravity-guiding" apparatus, swings his legs up, hooks the boots to the bar, drops his head down and hangs.

He swings back and forth, like a human pendulum, for several minutes -- then unhooks himself and starts his day. After work he repeats the swinging, and, if it's a "hard workout" day, lifts weights, does sit-ups and other exercises: all upside down.

If it's an "easy workout" day, he just hangs for 10 or 15 minutes (His longest hang was 20 minutes.) Sometimes he "swings" again before bed.

"Hanging corrects the ill effects of gravity pulling you down all day," claims Rush. He's heard -- but laughs politely just the same -- all the jokes about "hanging around" and the appropriateness of his name for his hobby.

"When you're right-side-up, gravity compresses and organs of the body downward, even flattens your brain in your skull. No wonder people get middle-aged spread and shrink when they get older."

A few "hanging breaks" each day, he maintains, "allows gravity to help the body re-correct itself. You stretch out and elongate your spine, get blood to the brain, invert your internal organs and take stress off the heart -- which usually has to pump uphill to the brain."

Devotees claim hanging cures everything from menstrual cramps to wrinkles. "People are skeptical at first," admits Rush. "But once they try it, it's hard to get them down."

Created more than 30 years ago by California osteopath Robert Martin to help cure back problems, the Gravity Guiding System is used by hospitals, universities, professional sports organizations and health clubs. (Hanging -- like any exercise program -- say the experts, should be started only after consulting with a physician.)

For years, back-pain sufferers from around the world have traveled to Dr. Martin's offices in Pasadena. But the general public's interest has blossomed only recently, since "American Gigolo" made upside-down chic.

Hanging is practiced by "thousands of people," says 71-year-old Martin, who trained as a gymnast before attending medical school. Among famous "hangers" he lists violinist Yehudi Menuin, body-builder Arnold Schwartzenegger and septuagenarian Laura Huxley, widow of Aldous Huxley.

Daily hangings nearly all his life, Martin claims, has added about three inches to his height -- from 5-feet-6 at age 20 to 5-feet-9 now. (Among people who come to him are those trying to meet military and police height requirements.) Both he and his wife hang for a total of 30 minutes each day, and all the Martin children have been hung upside down daily since birth.

One reason for hanging's burst of popularity, says Martin, is the high incidence of back problems. "On any one day 8.5 million Americans are in bed with a backache," he says. "Eight out of 10 human will have a crippling backache during their lifetime."

Even those who don't have back problems benefit from hanging, he says, to prevent back strain and to reverse other ill effects of gravity's constant downward pull. Exceptions, he says, are individuals with bone disease or retinal detachment.

While Martin says he has endorsement from numerous medical specialists, others aren't so enthusiastic. "It could cause problems for people with circulation trouble," says orthopedist Hans Kraus, a medical adviser to the President's Council on Physical Fitness and Sports.

"It might make back and leg problems worse," adds Dr. Kraus, who has seen pictures and pamphlets on gravity/inversion. "Frankly, I think it's sort of an unnatural way to take care of things that could be helped by natural means."

"Using gravity is the most natural thing there is," counters Dr. Martin. "The human fetus is inverted in the late stages of its development. Children often sleep in an inverted posture, by assuming a knee-chest position."

Rush says hanging has cured the "back kinks" he developed when he moved to Washington in 1975. "Sitting behind a desk all day was new to me. I've always enjoyed physical activity, I've run marathons, and hanging seemed like such a logical release."

In the four years since Rush bought his first pair of inversion boots -- which he saw while vacationing at a California spa -- he's taught about 60 people how to hang through an Open University course. He's also a representative for manufacturers of the equipment (boots, $78; portable gravity guider, $800, and stationary gravity guider, $1,300.) The boots, he says, can be used alone with any sturdy bar, playground equipment, or even a solid tree march.

Rush brought his portable equipment to the pool last summer, he says, and caused some excitment. "Everyone got silent and just stared." Among his converts are his 50-year-old mother and friends who often stop by his apartment to "hang out."

"I'm an addict," Rush admits. "If I'm away from it for awhile I miss the euphoria.

"Sure, people think it's strange. But what I see is that they're the sheep following the flock. It all depends on how you look at things. I guess you could say I've than most people. Maybe it's from spending so much time upside down."