Male circumcision, already shown to reduce the incidence of H.I.V. infection in men, also reduces transmission of both herpes simplex virus Type 2 and human papilloma virus, a study has found.

According to the Centers for Disease Control and Prevention, at least 45 million people in the United States ages 12 and older have had herpes, or H.S.V.-2, the incurable infection that can cause recurrent painful genital warts. About 20 million are currently infected with human papilloma virus, or H.P.V., which causes various genital cancers, including most cervical cancers. There is no treatment or cure for H.P.V., but there is a vaccine now licensed only for girls and women.

The study, a randomized clinical trial published Thursday in The New England Journal of Medicine, assigned more than 3,000 uncircumcised Ugandan men who were not infected with H.S.V.-2 to undergo immediate circumcision or to be circumcised 24 months from the start of the investigation. A subgroup was similarly evaluated for H.P.V. infection.

At 24 months, 114 men of the men initially circumcised and 153 of the noncircumcised tested positive for H.S.V.-2. After controlling for various health and behavioral factors, the researchers estimated that circumcised men had a 25 percent reduced risk of infection. The results do not apply to their partners.

For the types of H.P.V. that cause genital cancer, the results were even more striking. About 18 percent of circumcised men were infected at the end of two years, compared with almost 28 percent in the control group. Even after adjustment for types of sexual practices, symptoms of sexually transmitted infections and other variables, the circumcised men had a 35 percent reduced risk of infection.

The mechanism for the effect is unclear, but the authors suggest that the retraction of the foreskin during intercourse exposes the penis to infection, and that the moist area under the foreskin may then provide a protected environment in which the viruses can flourish.

Asked about the applicability of the African results to men in the United States, the study’s senior author, Dr. Ronald H. Gray, a professor of reproductive epidemiology at Johns Hopkins, said, “There is no reason to believe that this is in any way unique to Africa.”

The study confirms the results of two previous trials in South Africa, and Dr. Gray believes that taken together the studies have significant implications for public health.

“The findings suggest that there are important lifetime health benefits to the procedure,” he said. “I think it’s important that pediatricians consider the lifelong benefits that might accrue from circumcision when they are advising parents on whether the procedure should be performed in baby boys.”

Other experts agreed. Robert C. Bailey, a professor of epidemiology at the University of Illinois, Chicago, who has published widely on the subject, said the American Academy of Pediatrics and other professional associations “are not taking the lead in providing clinicians, nurses and midwives — the people who assist parents in making decisions,” with the information they need. “And so parents are not being fully informed,” he added.

An editorial published with the study said that rates of circumcision in the United States were declining, and that they were lowest among black and Hispanic patients, groups with disproportionately high rates of H.I.V., herpes infection and cervical cancer. There are 16 states in which Medicaid does not pay for routine circumcision, and this may exacerbate the problem among the poor, the editorial said.

The authors acknowledge that both intervention and control subjects were self-selected, and that compliant subjects might be at lower risk for infection to begin with. That could result in an underestimation of the effect. Since the men were evaluated only at 24 months, it also is difficult to determine whether the lower rate of infection was because of a reduced rate of acquisition or an increased rate of infection clearance.

Still, considering the results of their own and previous studies, the researchers conclude that circumcision should now be accepted as an effective intervention for H.S.V.-2 and H.P.V. prevention, even though they emphasize that the procedure is only partly effective and that the promotion of safe sex is still essential.