WASHINGTON, Jan. 23 (AP)  The government is considering raising standards for birth control drugs, saying new pills appear to be less effective at preventing pregnancy than those approved decades ago.

The Food and Drug Administration asked a panel of experts on Tuesday whether it should require new contraceptive drugs to meet a standard of effectiveness before approving them for sale. The panel is to meet again on Wednesday.

In documents on its Web site, the F.D.A. says newer contraceptives appear to be less effective  with twice the failure rate at times  than previous products, most likely because manufacturers have started using lower doses of hormones that stop ovulation.

“The very first pills were very high dose and carried risks of blood clots and cardiovascular problems that would be unacceptable to most women,” Amy Allina, program director of the National Women’s Health Network, said. “Today, most birth control pills are very safe for the vast majority of women.”