Medical experts issued new guidelines yesterday that, if adopted by doctors, could save thousands of American women from having to undergo Cesarean sections to deliver their babies.

The most significant recommendation states that most women who have a Cesarean section need not automatically deliver their subsequent children that way.

The guidelines, issued by a panel convened this week by the National Institutes of Health, reflect widespread concern that too many Cesarean sections are being performed in the United States.

The percentage of babies delivered by Cesarean section has more than tripled in the past decade, from 5.5 percent in 1970 to about 18 percent today. tMore than 500,000 Cesareans are performed by obstetricians each year, according to the National Center for Health Statistics.

If doctors heed the new recommendations, that trend will be reversed. "The rate is going to stop rising and go down, but I don't think I want to be pinned down to a number," predicted Dr. Mortimer G. Rosen, director of obstetrics and gynecology at Case Western Reserve University, who chaired the task force that prepared the guidelines.

The guidelines recommend a number of key changes in the way American doctors care for women during labor and delivery:

Repeat Cesarean sections: 98 percent of American women who have had one Cesarean now undergo the surgery for subsequent deliveries, because of the possibility that a scarred uterus may rupture during labor. However, most obstetricians now use a low, horizontal incision in the uterus that heals easily and rarely ruptures. The report states that it is now safe, or safer, for a woman who has had this kind of Cesarean to deliver vaginally during subsequent pregnancies.

Thus, the panel recommended that in hospitals where facilities for emergency surgery are available, women who have had this kind of Cesarean section should be given the option of vaginal delivery, where possible, during subsequent pregnancies.

Cesarean sections for abnormal labor: Much of the increase in Cesarean sections is for women whose labor does not progress normally, either because the baby is too large to pass easily through the pelvis or is in the wrong position, or because the woman's labor contractions are not strong enough.

However, abnormal labor, or dystocia, can often be improved by allowing a pregnant woman to move around, to sleep for brief periods, or by giving her medications. The report recommends that doctors be more persistent in trying these measures before resorting to surgery, unless there is a reason to believe the baby is in trouble.

Cesarean sections for babies in the breech position: During the 1970s, obstetricians changed the way they delivered breech babies -- those who come out feet-first rather than head-first. 1970, only 11.6 percent of these babies were delivered by Cesarean section, but in 1978, 60 percent were delivered by Cesarean section. The change reflected a belief that it was safer to deliver these babies surgically, as well as changes in the training of young obstetricians.

But the report states that vaginal delivery is safe for breech babies in certain positions, if the baby weighs less than 8 pounds, the mother's pelvis is normal and the obstetrician is experienced with such deliveries.

Behavior in the operating room: The experts strongly urged that hospitals liberalize their policies to permit a baby's father or another relative to be present in the operating room during a Cesarean section. They said childbirth classes should place more emphasis on the possibility of a Cesarean birth. And they recommended that healthy babies not be routinely separated from their parents right after birth.

Last year, the United States had the highest rate of Cesarean sections in the world, followed by Canada and some European countries. The dramatic increase during the past decade is attributable to many factors, including advances in medical care and electronic monitoring during labor, increased public concern about infant morality, the trend toward having smaller families and later pregnancies, and doctors' fear of malpractice suits.

In District of Columbia hospitals, the rate of Cesarean sections performed in 1978 ranges from 13 percent of births at Providence Hospital to 27 percent at George Washington University Hospital, according to figures supplied by the hospitals. This reflects the range at hospitals nationally.

Although medical progress has made the operation much safer, a woman is still two-to-four times more likely to die during a Cesarean section than during a normal vaginal delivery. There also is a greater risk of illness for both mother and baby following surgery than after a normal delivery.

The report emphasized that in certain situations -- such as bleeding, a very abnormal fetal position, severe illness of mother or baby or a sudden cutoff of oxygen to the baby during labor -- an emergency Cesarean section is not only necessary but life-saving. Rosen said that every hospital with an obstetrical service should be staffed well enough to require only 15 minutes' notice to perform the operation.

"The time of labor . . . is perhaps the most riskly day of our lives, except for the day we die," he said.

Both obstetricians and consumer groups at the conference hailed the recommendations, particularly the new guideline on repeat operations.

"We are comfortable with the necessity to look at the possiblity of vaginal delivery after a Cesarean section," said Dr. Ervin Nichols of the American College of Obstetricians and Gynecologists.

"They made it a litter clearer to physicians that it's OK to give it [vaginal deliveries in subsequent pregnancies] a try," said Jani Fairley of C/SEC, a consumer group for parents and health workers.