The government has been petitioned for an immediate halt to sales of the medicine prescribed to millions for the nausea and vomiting of pregnancy.

Studies -- including the manufacturer's own -- have failed to show that the two-ingredient combination sold as Bendectin actually works, as required by federal regulations, the Washington-based Health Research Group (HRG) told the Department of Health and Human services (HHS).

The rules invoked in HRG's petition require each component of a combination drug to make "a contribution to the claimed effects." The rules implement a 1962 law that compels manufacturers to document any claim of drug effectiveness with substantial scientific evidence.

In 1980, about 2.6 million Bendectin prescriptions filled by druggist were sufficient for 10 to 25 percent of the women who were pregnant.

As approved by the Food and Drug Administration, a unit of HHS, the Bendectin prescribing instructions recommended two or three tablets daily, meaning that a user would swallow 20 or 30 milligrams a day of the effective principal ingredient, an antihistamine/sedative called docylamine succinate, the HRG told HHS Secretary Richard S. Schweiker.

Bendectin's other ingredient, a vitamin called pyridoxine hydrochloride, drew sharp criticism from Dr. Sidney M. Wolfe and researcher Pauline Sobel of the HRG, a nonprofit unit of Public Citizen Inc.

Pyridoxine not only fails "to significantly improve the effectiveness of doxylamine, which, alone, is effective, but . . . actually detracts" from the usefulness of the antihistamine/sedative, they said.