The Food and Drug Administration on Wednesday allowed the first-ever sales and marketing of a kit of emergency contraceptive pills that women can take the morning after unprotected sex to prevent pregnancy.

The PREVEN kits will be available by prescription by the end of September, said Roderick Mackenzie, chairman and founder of Gynetics Inc. of Somerville, N.J., which won the first approval to advertise and sell morning-after pills.The FDA has long told women, and doctors, how to use standard birth control pills in this manner, and the agency last year gave out specific information about which pills and dosages were effective as contraception up to 72 hours after unprotected sex.

But Wednesday's approval, for the first time, allows a pharmaceutical company to advertise and to sell special morning-after packets that women can keep in their medicine cabinets.

"It's not only a scientific but an ethical advance," said Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania. "Women now have more options and have long deserved to have the rights to prevent unplanned pregnancies."

Anti-abortion groups, however, have criticized the method.

The morning-after pills are different from RU-486, the French abortion pill, which actually ends a pregnancy several weeks after it has begun.

Gynetics had said the company would market the emergency kit last year, becoming the first U.S. company to take action since the FDA approved using contraceptive pills for emergency birth control.

In February 1997, the FDA said six brands of birth control pills were safe and effective as morning-after pills.