Nine months after the formation of a mayoral commission to attack the problem, District health officials are bracing for a fight over the best way to reduce the city's high infant mortality rate.

Some officials are arguing that the city should spend less time worrying about curbing teen-age pregnancy and more time worrying about the babies who are born.

The issue has been brought to a head by the release of a report that is sharply critical of the care some private and public hospitals in the city provide the tiny premature infants who make up the majority of the babies who die in the city each year.

According to the report, prepared for Mayor Marion Barry's Blue Ribbon Commission on Infant Mortality, 94 percent of the babies who died in 1977 within a month of their birth weighed about five pounds or less, and half of them weighed less than 2.2 pounds.

The report, prepared by a committee of the city's federally funded physician peer review group, pointed out that the District's rate of premature births is triple the national rate, and said that many hospitals have been making less than an all-out effort to save some of those babies.

But the report is particularly troubling to some officials in the city's Department of Human Resources, because it comes from a doctors' group and backs up what earlier studies have shown -- that, in the words of the report, "the contribution of malnutrition and adolescent pregnancy was not quantitatively very large" to the high level of infant mortality.

Instead of focusing on preventing teenage pregnancy, the report urges that the city concern itself with saving the premature babies who are born -- at least until more is known about the causes of prematurity.

Up to now, the city has directed what efforts it has made on cutting down the number of teen-age pregnancies, pregnancies that traditionally are believed to lead to a higher-than-usual number of infant deaths.

But the new study found that not to be the case in the District in recent years. Instead, less than 14 percent of the babies who died in 1976 and 1977 were born to young mothers and fathers.

But when the federal government gave the city $2 million as part of an Improved Pregnancy Outcome Project, city officials earmarked a large part of that to programs designed to cut down on the rate of teen-age births -- a rate that was already dropping dramatically, apparently because of the availability of abortion.

The committee preparing the infant mortality study looked very carefully at the teen-age pregnancy question, said committee chairman Dr. Gordon Avery. It used a computer to plot two curves -- one for maternal age and one for infant deaths -- and compared them.

"Above the age of 15," said Avery, the director of newborn care at Children's Hospital National Medical Center, the "two curves were quite similar. While a birth to a 16 or 17-year-old is a social tragedy, there doesn't seem to be much increased risk to the fetus."

And that is what the fight will be about. If they city is going to make any progress in the infant mortality campaign with which Barry has aligned himself so closely, some members of his administration believe that campaign will have to be separated from the effort to curb teen-age pregnancies.

The message of the new report was brought home last weekend at Columbia Hospital for Women, where an obstetrician took a gamble and won.

Dr. John Herbert Niles said he used to believe that infants born after only 28 to 30 weeks gestation -- rather than the full 38 to 41 weeks -- do not survive.

Niles said he had had some "very strong conversations" in the past with Dr. John Scanlon -- the director of nwborn care at Columbia and a member of the Blue Ribbon Commission -- over what Niles said was the futility of trying to save such small babies.

But a week ago, after telling Scanlon that a mother in labor did not need a cesarean section because she was at most 26 weeks pregnant and her infant would have little chance of surviving, Niles helped her deliver a baby whose 1.7-pound weight indicated she was about 27 weeks pregnant. That baby is still alive.

So this Sunday, faced with a mother whom he thought was 26 to 28 weeks pregnant and about to deliver, Niles acted aggressively, performed a cesarean, and again delivered a 1.7-pound baby, who yesterday was breathing without the aid of a respirator.

"Would you have doon this a year ago?" Scanlon asked Niles after the delivery.

"I wouldn't have done it a week ago," Niles replied.