DURBAN, South Africa - Life expectancy in countries worst hit by Africa's staggering AIDS epidemic is expected to fall to around 30 within a decade - the lowest in a century - as the disease kills tens of millions more in its sweep across the continent.
The new estimate, released Monday, is the latest attempt to quantify the incredible breadth and effect of the epidemic on sub-Saharan Africa, where 15 million have died of AIDS and 25 million more infected people almost certainly will die in the next few years.
''It's hard to comprehend the amount of mortality we will see in these countries,'' said Karen Stanecki of the U.S. Census Bureau, which compiled the projections.
Stanecki presented the new figures at the 13th International AIDS Conference, a high-profile meeting being held for the first time in Africa, ground zero of the epidemic.
AIDS already has sharply reduced life expectancy in many southern African countries. For instance, in Botswana, where more than one-third of adults are infected with HIV, life expectancy is now 39 instead of 71, as it would have been without the disease. And the numbers are expected only to get worse.
Stanecki projected that by 2010, life expectancy will be 29 in Botswana, 30 in Swaziland, 33 in Namibia and Zimbabwe and 36 in South Africa, Malawi and Rwanda. Without AIDS, it would have been around 70 in many of those countries.
''These are a level of life expectancy that have not been seen since the start of the 20th century,'' she said.
Speakers at the meeting struggled for superlatives to describe the scope of this disease in the poorest parts of the globe, especially sub-Saharan Africa, where nearly three-quarters of all HIV-infected people live.
''The problem will get much worse before it gets better,'' said Dr. Roy M. Anderson of Oxford University. ''This is undoubtedly the most serious infectious disease threat in recorded human history.''
Dr. Kevin DeCock of the U.S. Centers for Disease Control and Prevention called the epidemic ''Africa's worst social catastrophe since slavery.''
Stanecki predicted that by 2003, the populations of Botswana, South Africa and Zimbabwe will begin to fall because of AIDS deaths and dropping fertility resulting from the epidemic. In those countries, the populations will drop between one-tenth and three-tenths of 1 percent. Without AIDS, they would have grown between 1 percent and 3 percent.
Stanecki said this is the first time the Census Bureau has projected negative population growth due to AIDS. The population growth of several other countries - including Malawi, Namibia, Swaziland and Zambia - will be near zero because of the disease.
Experts note that programs to educate people about condoms and other ways of avoiding infection clearly can work in southern Africa. Because of early efforts, the epidemic never occurred in Senegal, and Uganda has reversed its high infection level.
AIDS medicines have dramatically improved survival in the United States and Europe, but the drugs are simply too expensive and hard to deliver for most of the world's infected. Five drug companies have pledged to lower their prices in the developing world, but health officials in poor countries note they still lack the health care services necessary to offer the medicines to the sick.
On Monday, the Bill & Melinda Gates Foundation, created by Microsoft's founder, said it will spend $50 million in Botswana to strengthen that country's health care system. Merck & Co. said it will match the donation in Botswana, mostly by providing AIDS drugs.