The gloomy projections, announced at the 13th International Aids Conference in Durban, South Africa, contrasted with more encouraging statistics on the spread of AIDS among heterosexual teenagers in the United States. Authorities reported that growing numbers of American teenagers have been heeding anti-AIDS alarms by reducing sexual activity and increasing condom use.

Meanwhile, the Bill and Melinda Gates Foundation announced Monday that it will donate $50 million to the battle against AIDS in Botswana, and Merck & Co. said it will donate anti-AIDS drugs worth a similar amount. The Gates money will be used to build up the health infrastructure so that the drugs can be distributed efficiently.

Since the beginning of the AIDS epidemic, 11.5 million people have died of the disease in sub-Saharan Africa. About 5,500 now die of AIDS every day, but researchers predict that about 13,000 will die daily by 2010. AIDS now accounts for 21% of all deaths in the region, with malaria a distant second at 9.1%.