WASHINGTON — Emergency contraception — the morning-after pill — should be available without a prescription, on pharmacy shelves next to the aspirin and cough medicine, government advisers said Tuesday.

The nation's largest gynecologists group had urged the move, saying it would greatly increase women's ability to get the pills in time to prevent pregnancy: within 72 hours of rape, contraceptive failure or just not using birth control.

Used widely, emergency contraception could cut in half the nation's 3 million unintended pregnancies each year and in turn prevent hundreds of thousands of abortions, proponents told scientific advisers to the Food and Drug Administration.

"There is a public health imperative to increase access to emergency contraception," said Dr. Vivian Dickerson, president-elect of the American College of Obstetricians and Gynecologists.

The FDA's advisers agreed, on a 27-4 vote, that the Plan B morning-after pill should be sold over the counter. A key consideration, they cautioned, would be clearer wording on the package so that women understand:

Use it as soon as possible after unprotected sex. Although it's highly effective for 72 hours — cutting a woman's chance of getting pregnant by up to 89 percent — it works best in the first 24 hours.

Like other hormonal contraceptives, it does not protect against sexually transmitted diseases.

It is a backup contraceptive and should not be used instead of routine birth control.

Cost could deter some women from using emergency contraception too regularly. Each one-time-use pack today costs $20 to $30, about as much as a month's worth of regular birth control pills. It's not clear if the over-the-counter price would change.

Manufacturer Barr Laboratories promised a massive consumer education campaign, including a 24-hour hot line for advice on using the drug.

The FDA isn't bound by its advisers' recommendations but usually follows them.

Commissioner Mark McClellan said Tuesday that the FDA would make a final decision on the morning-after pill in "a matter of months."

Asked whether political considerations would be taken into account, McClellan said, "We have a lot of information coming in. It's very much a science-based process."

Morning-after pills have been sold by prescription in this country since 1998 under the brand names Plan B and Preven. Makers sought to sell only Plan B over the counter.

The FDA says emergency contraception is safe, having been used by millions of women here and abroad with few side effects. The question for nonprescription use, the agency says, is whether women will understand how and when to use it without professional advice.

FDA's advisers were persuaded by a study of 585 women that found more than 90 percent correctly took the first dose of Plan B in time.