"It is really quite remarkable what they found," said Dr. David A. Grimes, a USC scientist who has performed research on the drug. "We have defined, for the first time, a true contraceptive role for RU-486. I think it will revolutionize the way RU-486 is viewed in this country."

RU-486, the brand name for the drug mifepristone, is manufactured by the French company Roussel-Uclaf and its German parent company, Hoechst. It is used in some European countries, primarily France, as an abortion pill, but it has also been the subject of worldwide research for its possible promise in treating breast cancer, a form of brain cancer called meningioma, endometriosis, glaucoma and a metabolic disorder called Cushing's syndrome. Since June, 1989, under pressure from anti-abortion groups, the U.S. Food and Drug Administration has prohibited import of the drug for personal use. Research on RU-486 as an abortion-inducing agent, including Grimes' work at USC, was halted because of difficulty in obtaining the drug. Only a limited number of studies on RU-486-none on abortion-continue in the United States.

"(RU-486) is an antiprogestin, and we know how important progesterone is to implantation," said Dr. Carol Kurz, a Woodland Hills obstetrician and co-chairwoman of the Los Angeles Coalition for RU-486, an advocacy group. "It makes a lot of sense that it would be effective. And it's nice to hear it has fewer side effects."