The World Health Organization officially recommended circumcision as a way to prevent heterosexual transmission of the AIDS virus Wednesday, setting the stage for donor agencies to begin paying for the operation.

The group acted after three clinical trials in Kenya, Uganda and South Africa, overseen by the national health agencies of the United States and France, found that male circumcision reduced the risk of infection of men through heterosexual sex by about 60 percent.

No countries have yet adopted circumcision as part of their AIDS prevention plans, "but I hope this recommendation will lead some to do so," said Dr. Kevin De Cock, director of the HIV-AIDS department of the World Health Organization.

In some southern African countries with very high AIDS rates, such as Lesotho and Swaziland, De Cock said, he has already heard anecdotal reports that men were asking private doctors for the operation.

Large donors, including the Global Fund to Fight AIDS, Tuberculosis and Malaria, and the President's Emergency Plan for AIDS Relief, have already indicated that they will be willing to pay for circumcisions if countries ask for money and can demonstrate that the operations will be done safely and with the right counseling.

It is crucial, the health organization said, that men be taught that they can still catch the virus and pass it on even if they are circumcised, and so should still lower their risk further by having no sex or sex with fewer partners and by using condoms.

The organization's recommendation represents a triumph for a few public health experts who argued for years — in the face of skepticism from prominent scientists — that circumcision had a protective effect. They had noticed that AIDS rates were lower in African regions where it was common, such as Muslim areas. But, until the recent clinical trials, it was impossible to convince mainstream experts that the lower rates were not because of other factors, like polygamy or harsh sharia law penalties for extramarital sex.

"It's a big day," said Daniel Halperin, an AIDS researcher at the Harvard School of Public Health who was an author of a 1999 paper in the Lancet arguing that evidence for a protective effect could be found in many small surveys of African sexual habits. "They finally said what we suggested years ago."

The countries where the operation is likely to do the most good — those where AIDS prevalence is high and circumcision is low — are places like South Africa, Botswana, Swaziland and other southern countries that have, by African standards, good health care.

"They can do it safely," Halperin said. "It's surgery, but it's not brain surgery."