A D.C. Superior Court judge has overturned a jury's award of $750,000 to a 12-year-old girl whose family contended she was born with birth defects because her mother took the morning sickness medication Bendectin, ruling that there was insufficient evidence to support the jury's findings.

Judge Joseph M. Hannon ordered a new trial in the case at the request of the drug's manufacturer, Merrell Dow Pharmaceuticals Inc. of Cincinnati. In an opinion filed last week, Hannon ruled that studies presented at trial allegedly linking the drug to birth defects are inconclusive.

The jury verdict in May was the first major judgment against the company in more than 300 similar suits filed across the country in relation to Bendectin. It was the first to find the company negligent in marketing the drug after scientific evidence suggested it might cause a wide range of deformities in fetuses.

A Baltimore attorney for the pharmaceutical firm, Sidney G. Leech, said yesterday that he was "obviously pleased" with Hannon's ruling. The judge's order, he said, supports the company's position that no tests presented in the cases conclusively linked the drug with birth defects.

Bendectin had been prescribed for about 33 million women worldwide until Merrell Dow removed it from distribution shortly after the jury here reached its verdict. Company officials said the decision to stop selling the drug was unrelated to the jury's award to Mary Oxendine of Mitchellville, Md.

The attorney for the Oxendines, Barry Nace, said he would appeal Hannon's ruling. He called the judge's opinion "a disgrace that makes a mockery of a civil jury system. If it's allowed to stand," he said, "it would suggest that no individual could sue a drug company and expect to win in any case under any circumstances."

The opinion gave little detail about what flaws Hannon found in the jury's findings. His objections centered on animal tests, test tube analyses, epidemiological data and research on antihistamines that Nace argued had shown the company had been negligent in continuing to market the drug throughout the 1960s and 1970s.

Nace conceded at the four-week trial that while none of the individual data proved that the drug caused birth defects, a link could be shown when all the information was viewed together.

Hannon concluded that after reviewing the evidence, "no conclusion one way or another, can be drawn . . . "

Bendectin, introduced in 1956 by Richardson-Merrell Co., now a division of Dow Chemical Co., was the only drug approved by the Food and Drug Administration for use in treating the nausea and vomiting of early pregnancy.

The FDA has found no causal link between the drug and birth defects, but has continued to review animal data and human epidemiological studies. Of 13 such studies reviewed by the FDA, two have suggested that the drug may cause heart defects and cleft palates.

Since 1980, the FDA has warned women that Bendectin should be taken only for severe nausea and vomiting that cannot be treated without drugs.

No firm date has been set for retrying the case.

In overturning a jury's award in a lawsuit filed against the manufacturer of the drug Bendectin, a D.C. Superior Court judge ordered that a new trial be held only if his ruling is subsequently overturned by a higher court. The conditional nature of the order was omitted from an article Wednesday.