MEXICO CITY — While the world awaits findings from new AIDS prevention trials, millions of people are becoming infected because governments are overlooking studies showing that behavior modification works, AIDS experts said Tuesday.

Among the behavior modifications the experts cited: promoting safer sex through delayed intercourse and the use of condoms, decreasing drug abuse, providing access to needle exchange programs and promoting male circumcision.

But none of the measures alone offer a simple solution to preventing infection with H.I.V., the virus that causes AIDS, the experts said in a number of reports and news conferences at the 17th International AIDS Conference here.

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The experts said characteristics of the global epidemic varied greatly among and within countries, most of which were not focusing prevention resources where their epidemics were concentrated. 

Combining these measures and delivering them on a wider scale is crucial to reversing the global H.I.V. epidemic, they said.

Health workers have had initial successes in providing antiretroviral drugs to treat an estimated three million people worldwide. 

But tens of millions more people need the drugs, and additional millions are now becoming infected.

The world cannot treat its way out of the AIDS epidemic, many experts have long said, and a scientific debate exists over the extent to which antiretroviral therapy can reduce transmission of the virus. 

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A pressing need exists to combine H.I.V. prevention and treatment efforts, experts said Tuesday.

Researchers involved in each field “need to get married today,” said Dr. Myron S. Cohen of the University of North Carolina.  “We need to be one community.”

A 50-member panel known as the Global H.I.V. Prevention Working Group, which is supported by the Bill and Melinda Gates Foundation, released a report saying that prevention efforts must address a number of perception problems.

One is misplaced pessimism about the effectiveness of H.I.V. prevention strategies. 

A second is confusing the difficulty in changing human behavior with an inability to do so. A third is a misperception that because it is inherently difficult to measure prevention success, those efforts have no impact, the report said.

In the wake of three scientifically controlled studies showing that circumcising adult men helps prevent H.I.V. infection, some progress has been made in offering the procedure. 

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But no country has succeeded in fully educating its public about the benefits of circumcision, according to PSI, a nonprofit organization in Washington.

Dr. Adeeba Kamarulzaman of Malaysia said that outside Africa, about 30 percent of H.I.V. infections were among intravenous drug users. 

But because of stigma and a lack of resources, the world is failing to provide measures like methadone and needle sharing that can help such people.

Meanwhile, The Lancet, a medical journal published in London, released a series of papers on H.I.V. prevention to be published on Saturday.

“Behavioral strategies need to become more sophisticated,” and “that task is not easy,” 

Thomas J. Coates of the University of California at Los Angeles wrote in one article. In expanding prevention programs, 

he said, governments must be sure that they put in place “the right programs.”

Dr. Jorge Saavedra, who directs Mexico’s H.I.V.-AIDS program, said that national AIDS responses needed to involve more gay and bisexual men in planning ways to reach high-risk individuals. 

If political leaders do not follow the epidemiological and scientific evidence and direct efforts where they are most needed,

“we will lose the fight against H.I.V.,” he said.

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