The International AIDS Conference (search) opened Sunday with U.N. chief Kofi Annan (search) challenging world leaders to do more to combat the raging global epidemic and warning that women are increasingly the unwitting victims of the disease.

Three years after world leaders pledged at the United Nations to defeat the epidemic, there has been progress on many fronts, Annan said in a speech to nearly 20,000 policy makers, scientists, activists and celebrities.

"And yet, we are not doing nearly well enough," he said, in the first appearance by the U.N. secretary-general at an International AIDS Conference.

"We need leaders everywhere to demonstrate that speaking up about AIDS (search) is a point of pride, not a source of shame. There must be no more sticking heads in the sand ... no more hiding behind a veil of apathy."

Organizers criticized a U.S. decision to send a pared-down delegation that forced some researchers to cancel presentations, with delegates saying they believed it was a message that the conference wasn't focused enough on abstinence.

The U.S. stance sends "a strange signal" from the largest donor nation to anti-AIDS efforts, conference co-chairman Joep Lange said. "These ideological games are very counterproductive," he said.

The United States says the reason is cost cutting: It spent $3.6 million on the Barcelona trip. The bill this time is $500,000.

The conference was expected to discuss how best to prevent infections -- with discussions on whether to focus primarily on condoms, as host country Thailand has done, or on abstinence, as favored by President Bush.

"Bush tells lies, condoms save lives," read a placard held by one of an estimated 1,000 activists, many of them HIV positive, who rallied outside the venue to demand increased access to drugs, condoms and clean needles.

Thailand doled out condoms at tollbooths, hotels and the conference. The venue even had an exhibit of dresses made of condoms, symbols of the country's success in securing a sevenfold decrease in HIV infections since 1991 largely by promoting condom-only sex among prostitutes.

The emerging HIV epidemics of Asia typically have started with drug users and gay men, then progressed to sex workers and their clients, the region's main engine of transmission, said epidemiologist Tim Brown of the Hawaii-based East West Center.

The pace of the spread depends on the percent of the country's men who visit prostitutes, he said. Thailand had one of the higher percentages, about 20 percent in 1990, so its epidemic spread fast. The same pattern is happening more elsewhere in Asia -- but more slowly.

"What's particularly dangerous about the slow growth is that it won't motivate the kind of aggressive response that we've seen in Thailand and in Cambodia," Brown said.

A UNAIDS report issued before the conference said 38 million people worldwide are infected with HIV, 25 million of them in sub-Saharan Africa and 7.6 million in Asia. A record 5 million people were infected last year.

In sub-Saharan Africa, experts are alarmed at the high rates at which HIV is spreading from high-risk groups to young women and married, monogamous housewives.

Calling it a "terrifying pattern," Annan said women now account for nearly half of all adult infections, and in sub-Saharan Africa the figure is as high as 58 percent.

"And yet, one-third of all countries still have no policies to ensure that women have access to prevention and care," Annan said.

The theme of the 15th conference is getting more of the newly available antiretroviral drug combinations to the millions in the developing world who need them -- turning AIDS from a death sentence to a chronic disease.

In a speech to open the conference, Thai Prime Minister Thaksin Shinawatra urged governments around the world to provide ARV drugs to the needy. He announced a donation of $5 million over five years to a U.N.-initiated fund to fight AIDS.