A committee of outside advisers to the Food and Drug Administration concluded unanimously yesterday that no association between birth defects and the use of the "morning sickness" medicine called Bendectin is proved by existing studies.

At the same time, however, the panel expressed concern about two studies that, it said, suggest a possible association between Bendectin and congenital heart defects and cleft lips or palates. The panel said that these studies leave a residue of uncertainty about the popular drug.

The controversy over the drug, however, has centered on possible links between it and leg and arm disorders.

In two recommendations that appear likely to chill the prescribing of Bendectin, the only drug with specific FDA approval for use in the sensitive first trimester of pregnancy, the panel urged the agency:

To instruct physicians that Bendectin should be used only for significant nausea and vomiting unresponsive to non drug therapy, such as drinking very cold or very hot liquids and eating dry crackers or toast before rising.

Bendectin's labels included no such precautionary advice from 1956 -- when Richardson-Merrel Inc., without pre-marketing animal or clinical safety tests for the fetus, first began to sell Bendectin -- until 1977, when the company agreed to tell doctors that the drug should be taken in the first trimester "only when clearly needed."

Although the FDA approved Bendectin for the nausea "and" vomiting of pregnancy, the company has promoted it heavily for nausea alone. The number of pregnant women who feel nauseous but don't vomit is a much larger market than exists for combined nausea and vomiting.

To require that prospective users be given a so-called patient package insert stating -- in nontechnical language -- the essential facts also given to physicians.

In a third recommendation, the Fertility and Maternal Drug Advisory Committee, headed by University of Pittsburgh obstetrician-gynecologist David F. Archer, said epidemiological studies of Bendectin should be continued.

The FDA did not set a date for action on the panel's recommendations. Meanwhile, it faces hearings on its handling of Bendectin by the House subcommittee on oversight and investigations.

The panel's two-day session elicited highly diverse views. Some experts said Bendectin hasn't been shown to increase the risk of birth defects. Others said it is a weak birth-deforming agent. Yet others said existing studies are inadequate either to prove or disprove safety. Many of the scientists agreed that Bendectin should be available for women in whom nausea and vomiting may be so severe as to endanger them or their babies.

In the study of congenital heart defects, Dr. K. J. Rothman found an increased relative risk of this disorder in the babies of Bendectin mothers, but cautioned that the finding was "no more than exploratory . . . ."

In the study of cleft lips or palates, British epidemiologists Jean Golding and J. A. Baldwin matched 240 women whose babies had these anomalies with 480 "control" women with normal babies. Checking the prescriptions for all of the mothers, the scientists found that 12 whose children had clefts had taken the drug, compared with nine among the controls.

The product has been taken by or available to an estimated 30 million women. Since 1976, Bendectin has consisted of an antihistamine and a vitamin supplement. Previously it also included an antispasm agent that still is present in Debendox, the trade name under which the product is sold abroad, often over the counter.

U.S. physicians in 1978 wrote 3.8 million new and refill Bendectin prescriptions, with a wholesale value of $14.4 million.