Hundreds of thousands of American babies and mothers are being unnecessarily subjected to sometimes harmful electronic monitoring, then, sometimes, to needless cesarean operations during childbirth.

Another 165,000 pregnant women who could benefit each year from a prenatal test of their amniotic fluid to detect serious fetal malformations are still not being offered this revealing test.

These conclusions -- stated at the National Institutes of Health yesterday by members of three high-level obstetric task forces -- could have a profound effect on childbirth practices.

If prebirth taps of amniotic fluid -- or amniocentesis -- are increased in number, the consequence could be an increased demand by parents for abortions to prevent the birth of severely retarded or defective children.

The NIH task forces were assembled to develop concensuses on several controversial features affecting the three million babies born in the country each year.

The conclusions were stated partly in documents, partly in interviews as the three-day conference closed. Some of the most important ones were unstated on paper, yet would be clear to doctors.

For example, said one task force member, "The electronic fetal monitoring is a marvelous thing but in some hospitals -- or on some doctors' patients -- it's being done 101 percent of the time.

"We're saying, 'That's too much! At least two-thirds of the time it's usually not necessary. You won't be guilty of bad medical practice if you don't do it, and you can defend yourself if a patient, or a patient's mal-practice lawyer, accuses you of not doing 'everything' if there should be a bad outcome.'"

Electronic fetal monitoring -- or EFM -- usually consists of a combination of methods, external and internal, to measure fetal heartbeats and maternal labor contractions to guard against "fetal distress" -- most seriously, faulty heartbeat and lack of enough oxygen to feed the baby's brain.

The internal monitoring can include taking blood samples from the baby's scalp, attaching a clip to the scalp to record heartbeat and inserting an instrument into the mother's uterus to record such contractions.

The NIH 14-member fetal monitoring task force -- formerly the Task Force on Predictors of Fetal Distress headed by Dr. Frederick Zuspan of Ohio State University -- unanimously agreed that:

Simply listening to the heart with a stethoscope -- done by a well-trained nurse or doctor every 15 minutes early in labor, every five minutes later -- is sufficient to detect problems in most babies, though many doctors have argued otherwise. Present evidence shows no effect in most births of EFM on rates of infant death, disease or retardation caused by lack of oxygen.

Only in "high-risk" patients -- 25 to 35 percent, said Dr. Duane Alexander of NIH -- has routine EFM actually saved lives and prevented birth disorders. High risk conditions include low birth weight of the fetus, premature or late labor, a mother's illness [like diabetes or high blood pressure], use of the chemical oxytocin to start labor, abnormal fetal heartbeat and other complications.

EFM may be justified in a low risk fetus in some cases -- for example, Dr. Zuspan said, in a hospital with only three nurses and 10 beds suddenly filled with mothers in labor, or a hospital without expert obstetric nurses. But a hospital without well trained personnel should not be offering obstetric services at all, the task force added.

EFM can cause harm in a small number of cases, mainly infections, but also other problems, like abcesses on infants' scalps, with the deaths of approximately 1.2 babies per 2,000 fetuses monitored.

Also, though records at some large hospitals show no increase in cesarean operations, with some inevitable risks, caused when doctors become correctly or incorrectly alarmed by monitoring signals, task force members agreed that there has been "some" unnecessary increase.

"I can't say how much," said Dr. Raymond Neutra of the University of California at Los Angeles. "We just don't know."

The task force urgently recommended studies to find out, as well as more controlled studies of EFM's value before other new, expensive and sometimes risky procedures are widely adopted.