The Food and Drug Administration has asked the Bureau of Alcohol, Tobacco and Firearms to require labels on alcoholic beverages warning women that heavy drinking during pregnancy may cause birth defects in their babies.

In a letter dated Nov. 15 and released yesterday, Commissioner Donald Kenedy told bureau director Rex D. Davis, "Quite frankly, if the FDA retained jurisdiction over the labeling of alcoholic beverages, it would waste no time in commencing proceedings to require labeling warnings" for pregnant women.

"This is a problem not only for women who habitually abuse alcohol but also for those who consume alcohol in moderation but might occasionally inbibe more than two drinks a day," Kennedy said.

A spokesman for the Distilled Spirits Council, which represents producers and importers, said the scientific evidence is inconclusive regarding moderate drinkers. And he said the people whose babies would be harmed by so-called fetal alcohol syndrome are alcoholics for whom warning labels would be ineffective.

"The place a woman should go for advice when she's pregnant is not to the label of a liquor bottle but to her physician," he added.

A spokesman for the alcohol bureau's Davis, who was out of town, said the letter had been turned over to the general counsel's office for study.

An FDA spokesman said the agency agreed nearly 40 years ago to let the Treasury Department's alcohol bureau regulate alcoholic beverages to avoid the problems of two agencies overseeing the same product. The FDA since has tried to abrogate that agreement and require ingredient labeling on alcohol beverage containers. But it has been rebuffed by the courts.

The National Institute on Alcohol Abuse and Alcoholism warned last June that women who take more than two drinks a day during pregnancy risk giving birth to mentally retarded and physically deformed babies.