In the north wing of George Washington University Hospital, above the weekend clamor of Pennsylvania Avenue traffic, a rotating staff of some 20 doctors, nurses, respiratory technicians and orderlies ply the doll-sized instruments of their trade these days among 18 miniature clients.

The physicians are neonatologists--specialists in care of the newborn--whose charges this week include the first quintuplets ever born successfully in the nation's capital.

The quints--a 2 pound, 4 ounce daughter and four slightly larger sons born Tuesday to Daniel and Pamela Pisner of Olney, Md.,--are the unquestioned stars of the 18-bed intensive care nursery: tiny symbols of a 10-year revolution in the fragile science of birth.

So small are they that the total blood supply of each would scarcely fill a 3-ounce juice glass. So unformed are their responses that they sometimes forget to breathe.

But in the biophysical wonderland of neonatology--a medical speciality formalized only eight years ago--the quints are relative heavyweights, more than holding their own.

A hospital spokesman said yesterday the quints continue to progress satisfactorily. And while some have received oxygen to combat the sort of respiratory problems that commonly affect as many as half of all premature babies their size, a hospital spokesman said, none had needed or received "radical treatment" for any life-threatening situation.

Ten years ago, said Dr. Maureen Edwards, GW's director of newborn services, "We used to say that 75 percent of all babies under 1,500 grams (3 pounds, 5 ounces) at birth would die, and those that lived would live with some residual problem.

"Now of those between 1,000 and 1,500 grams, we can usually save 90 to 95 percent without any after effects at all."

Edwards hesitates a bit to quote such statistics.

In the first place, she said, "little babies do die. They can go from well to life-threatened so fast you can't believe it . . . faster than any adult ever could."

In the second place, she said, "we try to treat each life as unique. If it's your baby that can't be saved, the general statistics aren't much comfort."

But the truth is that the frontiers have changed, she said: "People tend to think of a 3-pound baby as hardly there. But for those of us who deal with premature babies all the time, 3 pounds is a pretty good size."

Many of the advances have come in biopharmacology--in the science of drugs used to delay the onset of labor so the quints could make it through their 30th week in the womb.

Others have come through the miniaturization of aerospace technology, producing such feats of lilliputian engineering as an intravenous medication pump capable of metering out a single cubic centimeter of medication evenly over the course of an hour.

But the biggest, she said, have come through the simple accumulation of specialized knowledge and support services--a whole range of doctors, nurses, respiratory therapists and even pharmacists attuned to the specialized needs of the newly born.

Premature infants, she says, are prone to a whole battery of physical problems, most of them caused simply by meeting the outside world before their bodies' immune systems are ready.

One of the most common problems is hyaline membrane disease, which killed President John F. Kennedy's youngest son 20 years ago. A healthy human lung, Edwards said, secretes a soapy substance which helps keep open the tiny air sacs in the pulmonary tissue. But since they aren't needed in the womb, the lungs don't begin such secretions until about the 35th week of gestation.

Breathing without them requires more effort for the baby, which doctors alleviate by boosting the oxygen content and sometimes the actual pressure of the air the baby inhales.

The strain of the breathing uses up more calories, tending to exhaust the baby's meager nutritional resources when he needs them most to put on weight. Very small babies have stomachs and digestive systems too minute to process food. For years they needed a greater volume of intravenous feeding than could be channeled through their small veins, but the development of fat and protein which can be administered intravenously now permits injection of more calories to the ounce.

Feeding, however, can still be a problem. Doctors must use needles and tubes not much larger in diameter than a piece of thread, attached to veins in the feet or scalp.

Even those who should be able to eat sometimes haven't yet developed a suck-and-swallow reflex, which nurses try to nurture with miniature pacifiers. Sometimes that works, sometimes not.

But the most frightening and yet wonderful thing about working with premature infants, Edwards said, is watching the gradual coordination of a baby's physical systems as they stop and sputter and gradually surge to life together like the uncertain cylinders of a tiny engine.

"They stop breathing all the time," she said. "Sometimes they just forget. Or maybe a baby has put his head down on his chest so low it cuts off his windpipe. He's not too smart yet, and he has to figure out that's not a good idea.

"Or maybe he's having a stool and he hasn't yet figured out how to do two things at once."

Heartbeat monitors on the transparent incubators warn nurses at such times. Often just the touch of a hand is enough to get the baby breathing again. Sometimes they use a baby respirator, not much larger than the bulb of a perfume atomizer.

"Without the nurses, we couldn't do anything," Edwards said. "We could do without the equipment and the doctors, but not the nurses. They're not always easy to get and to keep. It's harder and harder these days to get people into the traditional female roles.

"There's a lot of pressure because babies don't all get well, and when they don't there's a lot of sadness. But there's a lot of life, too."