Using a surgical technique that could one day help human babies, scientists are taking monkey fetuses from the womb, operating on them, then returning them to their mothers to be born at the normal time.

The federally financed research --which practitioners say could lead to dramatic repairs of human abnormalities before birth -- is being done at two Washington-area laboratories and one at Harvard University.

The technique's success undercut the belief, once widely held in medicine, that if a womb is cut open, a pregnancy will usually end.

"That isn't true," Dr. Edward Taub, director of this work at the private, nonprofit Institute of Behavioral Research in Silver Spring, said last week.

"We've removed some fetuses two-fifths of the way through gestation" --that is, pregnancy -- "kept them on the operating table for nearly two hours for our studies, then brought them to normal term," he explained.

"I think the old assumption was that if you opened the uterus, the fetus would almost automatically be aborted. But people simply hadn't tried."

What is more, he said. "We've kept animals alive three years after birth. This is like nine years in a human being. These animals remained entirely normal except for the deficits (injuries) we induce in our operations to learn about fetal development.

"There was no indication these animals would not have led a perfectly normal life span."

Now, he added. "I think we're on the verge of a new era of what might be called 'fetal neuropsychology'," or the study of the way the fetal nerve system and brain develop and produce behavior.

Other researchers have studied other fetal developments in ways that would have been impossible by other methods. So the field may become not just the study of the brain and nerves but one covering all areas of fetal growth -- and, in time, ways to correct abnormal growth to make a normal infant.

Getting to this point has taken nearly two decades of effort.

The first work was done in the early 1960s by two professors of obstetrics, Dr. Albert Plentl of Columbia University and Dr. D. L. Hutchinson of the University of Pittsburgh. Both brought some monkey infants to normal birth after removing them from the womb, then returning them.

But the largest sustained effort with a high degree of success -- both in keeping the fetuses alive and advancing knowledge -- was made by Dr. Ronald Myers of the National Institute of Neurological and Communicative Disorders and Stroke, part of the National Institutes of Health in Bethesda.

Starting in 1964 at an NIH laboratory in Puerto Rico, Myers and colleagues did fetal surgery on "from 25 to 30" developing monkeys, with what he described last week as "a success rate varying from 40 to 70 to 80 percent." That is, that many of the fetuses were brought to term, or normal birth, with the number varying according to the rigors of the experiments.

For Myers' goal was not just survival but knowledge. For example, he clamped the umbilical cords of fetal monkeys halfway through gestation. According to a report in Science magazine, he was thus able to study the effects of depriving the brain of oxygen.

To the placenta, the organ through which the mother and fetus exchange many materials, and on subsequent fetal growth. Myers showed that undersized primate babies -- almost certainly including human babies, since humans are primates -- are not necessarily premature babies but are sometimes babies who have lacked enough oxygen.

"This was very interesting and also important," he said in an interview. "Up to then it had been assumed that any small newborn baby was premature. And if the mother had given a date nine months earlier for onset of pregnancy, it was assumed she was wrong. We showed she wasn't necessarily wrong."

A few people elsewhere did similar work, some at the University of Oregon Primate Center. Myers turned to other methods, but first taught the technique to Taub.

Now Taub, with Drs. Gilbert Barro, David Martin (of Litton-Bionetics Laboratories in Rockville) and Michael Goldberg (of the Medical College of Pennsylvania), has done fetal surgery on 36 developing monkeys, with a 33 percent success rate.

By cutting various nerve roots, the Taub group has abolished sensation from different parts of the developing body. And it has learned that -- despite the devastating loss of sensation and sensory feedback -- these monkeys as infants exhibit nearly normal limb movements.

"In short," Taub said, we've learned that these motor patterns do not necessarily depend on sensory feedback, as often proposed, but are instead parts of the animals' genetic endowment."

Taub taught the methodology to Dr. Patricia Goldman, who is part of a National Institute of Metal Health group working at NIH.

The group is removing parts of the fetal brain to study effects on later learning, and has found that even when much of the prefrontal cortex, an area considered vital to learning, is removed (at the two-thirds point in gestation), the monkey infant can later learn normally.

Dr. Pasko Rakic of Harvard Medical School has studied the development of vision in fetal monkeys. "But the number of people doing fetal surgery is still few," Myers said. "I think it has a great deal to do with the fact that federal funding of research today is too low. I think a lot of people don't have the money to take advantage of the method."

Taub -- whose work has been financed by $300,000 in grants from NIH's National Institute of Child Health and Human Development and the W.T. Grant Foundation -- agrees.