Circumcision substantially decreases a man’s risk of becoming infected with the AIDS virus by a woman, but acceptance of the procedure has been slow in Africa, where it would do the most good. There’s also evidence that some people overestimate circumcision’s protective effects — a potentially dangerous and unintended consequence of campaigns promoting it.

Those are among the findings presented at the 19th International AIDS Conference here this week.

As a medical procedure, circumcision is simple and becoming simpler. New research shows that nurses can perform it safely after three days of training, and it can be done in assembly-line fashion using devices that don’t require scalpels and stitches.

Although circumcision’s effect on protection against HIV is clear — three studies have shown a 60 percent reduction in risk to men — as a public health strategy, it is fraught with caveats.

Many ethnic groups have strong cultural traditions against the procedure. In adult men , circumcision requires six weeks of sexual abstinence while healing. And, its protection isn’t complete enough to allow men or women to forego other forms of protection, such as condoms. A woman having intercourse with an infected man is less likely to become infected if the man is circumcised, but the degree of protection remains uncertain. Also, there is no evidence that circumcision protects gay men practicing anal intercourse in any way.

Nevertheless, many AIDS researchers and advocates view it as a strategy that needs far more promotion since it provides some protection to men having sex with infected women.

“It’s not a perfect solution, but it’s a critical piece of the fight against HIV/AIDS,” said Mitchell Warren, executive director of AVAC, an advocacy organization.

Fourteen African countries are targeted for increased circumcision efforts. Non-medical circumcision is a ritual of attaining manhood for some ethnic and tribal groups. It also is widely practiced in Islamic populations.

International health agencies have set a goal of having 80 percent of males between ages 15 and 49 circumcised by 2015. That would require 20 million circumcisions. Only 1.5 million have been done in the five years since the World Health Organization recommended it in countries with a high rate of HIV infection.

But, the obstacles are numerous. The procedure costs $65 to $95, with an additional cost of about $60 for health system overhead. In some countries it must be performed by physicians, making “task shifting” — the assignment of certain duties to less expensive practitioners — impossible. In Uganda, for example, it will require an act of parliament to allow nurses to perform circumcisions, said Angelo Kaggwa, a Ugandan working with AVAC.

Studies show that many African men are willing to become circumcised, and in some areas many have recently gotten the procedure.

In Nyanza Province in Kenya, 50 percent of men originally randomly assigned to not be circumcised in one of the clinical trials have chosen to have the procedure in the five years since the study ended. Follow-up shows that circumcision has reduced their chances of becoming infected by 65 percent — essentially the same amount as found during the study.

In Orange Farm, a region of South Africa where another study was done, circumcision prevalence has increased from 17 to 54 percent in the past three years. HIV infection rates remain very high there, and the protective effect is dramatic — 19 percent of uncircumcised men are infected, compared to 7 percent of circumcised ones.

Researchers estimate that HIV prevalence in Orange Farm would be 20 percent higher today if the circumcision study and uptake afterward hadn’t occurred. More than 1,000 HIV infections in men have been prevented. Bertran Auvert, of the University of Versailles, said that “we think it is just a matter of time” before HIV incidence in women declines because fewer men will have the virus.

So far, there is little evidence of “risk compensation” after circumcision — doing riskier things because of a feeling of being protected. Kenyan researchers interviewed 101 women whose male partners were recently circumcised. Eighty-four percent said they had little or no chance of being infected, with 38 percent attributing that to circumcision. They were five times more likely than men to think that using a condom was no longer necessary, and three times more likely to say they might take on another sex partner.

“Women are more likely to think themselves protected, and more likely to be willing to participate in risk-compensating behavior,” said Timothy Okeyo Adipo, a Kenyan researcher who presented the data. The few studies done of actual behavior, however, have found that it changes little after circumcision.

Risk compensation also concerns anti-circumcision protesters who have stationed themselves in front of the Walter E. Washington Convention Center, toting posters with calls such as “Intact Genitals are a Human Right” and “Circumcision is Torture.”

The activists, who represent several different groups, share the concern that male circumcision discourages men from wearing condoms vigilantly because of a belief that the procedure alone provides full protection from HIV infection. This false sense of security, they said, could increase the spread of HIV instead of inhibiting it.

“If you circumcise men, they lose sensitivity, and are then even less likely to wear a condom,” added Danelle Frisbie, a former sex education teacher at the University of Northern Iowa and co-founder of a non-profit infant health group.

She expressed concern that the studies presented at the conference “only told one side of the story,” though she did not comment specifically on the three randomized control trials.

Frisbie was also concerned with infant medical male circumcision in the United States, calling it a human rights violation. “We’re all born with the right to our whole body,” she said.

Alyssa A. Botelho contributed to this report