The Food and Drug Administration Friday told drug companies how to label most over-the-counter drugs to warn pregnant women and nursing mothers they should seek advice before taking them.

With the exception of a single word, the agency stuck with the message it proposed in September -- but not for lack of suggested alternatives.

In final form, the agency's warning reads: "As with any drug, if you are pregnant or nursing a baby, seek the advice of a health professional before using this product." The word "health" was added for clarity.

The FDA's language, an official said, was distilled from several versions that had bounced around the agency. And with a certain pride of authorship, it rejected alternatives offered in the 60 sets of comments it received.

Among them:

* "A small number of drugs have been conclusively shown to a degree of scientific certainty to have adverse effects on the developing fetus. However, information of this type is not adequate to establish that this drug is safe for the developing fetus." ("Not apt to be understood by the average consumer," the FDA said.)

* Adding "CAUTION: This drug has not been proven safe for babies before or after birth." (The commenting person felt the phrase "seek the advice of a health professional" masked the potential danger of the product to a pregnant woman. "Redundant," the FDA said.)

* "If you are pregnant or nursing a baby, you should seek professional advice before using this or any other drug product." (The commenting person suggested this was more grammatical than the FDA's version, but the agency said the emphasis wasn't the same.)

The agency also rejected the idea of requiring manufacturers to include symbols to convey the message to women who don't speak English. But it agreed that warning labels would not be required for drugs not absorbed by the body, such as toothpaste and lip balm, and drugs intended to help the fetus or nursing infant. Manufacturers will have until Dec. 5, 1983, to change their labels.