She said the agency had drafted new rules intended to assure that women would be included in nearly all tests and that their numbers would be sufficient to tell differences in how men's and women's bodies reacted to a drug.

The chief effect of not having such data has been that drug doses for women were sometimes wrong, to the point that they made the drugs useless or worse, F.D.A. officials say. For example, it was not known until recently that oral contraceptives could sometimes block the effects of other drugs or that other drugs could prevent contraceptives from being effective.

Many drugs act very differently in women's bodies. For example antidepressants and tranquilizers are absorbed at a different rate by women than by men, meaning the doses for women should be different.

In one case it was found that an antidepressant drug caused more far more seizures in women because of different absorption patterns and that lower doses could be effective without causing seizures. Question of Proportions

Dr. Kessler said that if researchers and companies did not include enough women, "we reserve the right not to approve their applications." He added that "it should never come to that," because including women was relatively easy and would not necessarily increase the number of people needed for tests, but rather the proportion of them that were women. That means drug companies' costs for the tests would not be significantly increased.