After MSF introduced AIDS treatment in Khayletsha, a poor township outside Capetown, the number of women getting tested for HIV tripled in two years, as did the number of condoms distributed, according to Mr. Achmat. In Haiti, a team of Harvard doctors led by Paul Farmer documented similar results.

That question will be the centerpiece of the coming World AIDS Conference, which will draw more than 10,000 AIDS researchers, activists and physicians to Barcelona starting this Sunday (July 7). The clash between proponents of AIDS treatment and those who favor focusing on prevention will profoundly affect how most of the US$2 billion Global Fund to Fight Aids, Tuberculosis and Malaria will be spent.

"Everyone's duking it out for the little money available," says Rachel Cohen, a representative for the humanitarian group Medecins Sans Frontieres.

Meanwhile, the number of lives at stake continues to climb. New projections from the United Nations' AIDS program, UNAIDS, issued Tuesday, estimate that among the hardest-hit countries, 68 million people will die between 2000 and 2020, five times the toll of the epidemic's first 20 years. "From a historic perspective, we're still at the beginning of the AIDS epidemic," says Peter Piot, UNAIDS's Executive Director.

Both sides agree the pot of money available is paltry. UNAIDS estimates that by 2005, US$9.2 billion will be needed annually to provide an expanded response to HIV/AIDS in low and middle-income countries, including US$4.8 for prevention and $4.4 billion for treatment and support.

Many public-health officials, as well as Bill Gates, chairman of Microsoft Corp. and benefactor of the richest foundation in the world, insist that money spent on prevention will save the most lives. But activists and many researchers in the field are demanding that much more of the fund be spent on medicines treating those already infected.

Poor governments such as those in sub-Saharan Africa, are hobbled by limited health-care budgets even as the disease claims many of their most productive citizens. About 10 million of the world's 40 million people infected with the virus, will be sick enough to require treatment in the coming two years. Nearly three-quarters of those who have HIV live in Sub-Saharan Africa, ground zero of the epidemic.

Against this backdrop, treatment advocates, doctors, and patients are planning research presentations and massive protests in Barcelona. They also are gearing up to create "a new pan-African treatment movement, demanding everything from vitamins to antiretrovirals," says Zackie Achmat, a leading South African activist.

"It's relatively simple to say dollar for dollar that prevention is more cost-effective," says Chris Collins, director of the AIDS Vaccine Advocacy Coalition. "The more complex point is what happens in societies where one in five or one in three people in the professional class are wiped out?"

Medecins Sans Frontieres, or MSF, for instance, will present clinical data showing about 750 patients in poor regions of the world responded significantly to AIDS-drug therapy; the medicines, doctors say, had a "Lazarus effect."

Meanwhile the pharmaceuticals industry is relieved by the shifting focus of the debate. The rancorous split has various AIDS factions fighting each other rather than lambasting drug makers over the price of AIDS drugs.

A new target of criticism is Mr. Gates and his Foundation, which is staunchly backing the prevention side with hundreds of millions in funding and Mr. Gates's personal influence. Though Mr. Gates will stay away from Barcelona, a new "prevention task force," led by his top AIDS-prevention expert Helene Gayle, formerly of the U.S. Centers for Disease Control and Prevention, will be taking center stage.

Dr. Gayle is focusing the foundation's substantial global-health resources almost solely on prevention, including condom use, behavioral changes, voluntary testing and counseling, vaccine and microbicide research and methadone and needle exchange programs.

"Our priority is prevention, because it has the best long-term impact," Dr. Gayle says.

She is hardly alone. A soon-to-be published scientific report estimates more than 45 million people will be infected by 2010 - but that number could be slashed by two thirds if proven prevention methods were funded and implemented now.

Twenty years after the AIDS virus was first identified, huge gaps in knowledge, especially among young people, are pervasive.

A report by UNAIDS and the U.N.'s International Children's Education Fund in countries with generalized HIV epidemics, such as Cameroon, Central African Republic and Sierra Leone, more than 80% of young women ages 15 to 24 don't know enough about HIV. In Ukraine, although 99% of girls had heard of AIDS, only 9% could name three ways to avoid infection.

Another study, recently published in the medical journal the Lancet, estimates prevention is 28 times more cost-effective than the AIDS-drug cocktails. To do anything other than give the vast majority of money to prevention is "public-health malpractice," says Elliot Marseille, the lead author of the study.

Opponents disagree. "It's relatively simple to say dollar for dollar that prevention is more cost-effective," says Chris Collins, director of the AIDS Vaccine Advocacy Coalition. "The more complex point is what happens in societies where one in five or one in three people in the professional class are wiped out?"

Social upheaval caused by mass deaths from AIDS could make it harder to prevent new infections. For example, research shows that when AIDS strikes rural families, it leads to hunger because there are fewer able-bodied people to work the land. Moreover, hungry women and girls are much more likely to sell sex for money, thus fueling the epidemic.

Some 2.2 million people died of AIDS in Africa last year and 28.5 million are infected. By contrast, in high-income countries, about half a million people are taking the so-called antiretroviral drug cocktails and 25,000 people died of AIDS in 2001.

In South Africa, "despite a 99.9% focus on prevention by the government, the infection rate has continued to increase," says Mr. Achmat, of the Treatment Action Campaign, a leading nonprofit group pushing the new drive for an African-treatment movement that includes churches, union officials, lawyers, physicians and patients.

He points to an MSF project as a new and better model for slowing the spread of the disease by linking treatment and prevention.

After MSF introduced AIDS treatment in Khayletsha, a poor township outside Capetown, the number of women getting tested for HIV tripled in two years, as did the number of condoms distributed, according to Mr. Achmat. In Haiti, a team of Harvard doctors led by Paul Farmer documented similar results.

"To think you can step over all those infected people and effectively do prevention is B.S.," says Eric Goosby, director of the Pangea Global AIDS Foundation, which is running treatment clinics in Rwanda.

But economists argue that linking prevention and treatment is expensive. They also say it will take many years to build up the capacity to treat AIDS patients in the developing world.

Despite steep price cuts for AIDS drugs, progress in getting the drug to those who need it has been slow for a variety of political and logistical reasons. For most people in poor countries, even at cut-rate prices the drugs still cost too much. UNAIDS estimates that in Africa, about 30,000 people overall have access to AIDS drugs, including the rich and poor.

That may seem like a lot compared with two years ago, when about 2,000 to 3,000 - mostly white South Africans - were taking such drugs. But 2.2 million people died of AIDS in Africa last year and 28.5 million are infected. By contrast, in high-income countries, about half a million people are taking the so-called antiretroviral drug cocktails and 25,000 people died of AIDS in 2001.