Population experts now believe that several African countries may achieve zero population growth in just a few years. But family planners are not cheering.

The reasons are gruesome and worrisome: populations devastated by AIDS and further threatened with food shortages, water depletion, ecological collapse and social chaos.Family planners have been trying for decades to halt the population explosion in countries projected to double or triple populations by 2050. But they didn't want it to happen this way. They don't want allies that kill and destroy societies.

"A lot of countries will not see expected population increases because of rising death rates," said Lester Brown, president of World Watch and author of a new report on world population problems.

Revised U.N. projections for population growth will be out at the end of October, and U.N. demographers confirm that the impact of AIDS in some African coun-tries will be dramatic, even "unbelievable."

AIDS, which killed 2.3 million adults and children last year, will not slow worldwide population growth, however. That will reach 6 billion by the middle of next year and is expected to rise to between 7.7 billion and 11 billion by 2050.

Hardest hit by AIDS is Zimbabwe, where 25 percent of the population now carries the AIDS virus. Brown estimated its population will stop growing and possibly begin declining in just four years.

Current U.N. projections, made in 1996, have Zimbabwe more than doubling in population, from 11 million to 24.9 million, by 2050.

Larry Heligman, assistant director of the U.N. population division that draws up long-range projections, said demographers are closely watching deaths from AIDS in 34 countries. These include countries where the infection rates have hit 2 percent or where the affected population is large, such as India which has more than 4 million of the world's estimated 30 million people now infected by the virus.

"When you begin to look at the projections beyond 2005, what we are seeing is just unbelievable," Heligman said in an interview. He said some revisions were made in projections two years ago because of AIDS, but the 1998 impact will show "even stronger devastation."

Ironically, alarm over the impact of AIDS on population in the worst-hit countries comes as the spread of the virus has leveled off or declined in the United States and other wealthier countries and is slowing even in some poorer countries: Thailand, Brazil and Uganda, for example.

Fueling the concern are the first detailed global figures on AIDS infection percentages released at an international AIDS conference in June. In addition to the impact on Zimbabwe, the U.N. data show Botswana with 25 percent AIDS infection, Namibia with 20 percent, Zambia with 19 percent, Swaziland with 18.5 percent and several other African countries with 10 percent or more.

By contrast, the AIDS infection rate in the United States is 0.57 percent. The global rate also remains below 1 percent.

Groups working to control rapid population growth worldwide are concerned the new projections will be viewed as support for the cynical view that the world's problems will take care of themselves no matter what humans do.

"We must not let people think that an epidemic is going to solve problems. It's going to worsen them," said Amy Coen, president of Population Action International, which conducts research and supports efforts to slow population growth worldwide.

Coen, in an interview, noted that AIDS usually hits people in the prime of life, in their most productive years. In some countries, the number of AIDS orphans - children who have lost both parents to AIDS - is in the hundreds of thousands.

In Uganda, where the impact of AIDS is acute despite recent gains, there are 1.7 million AIDS orphans.

Brown, in his Worldwatch report, cites a number of pressures in addition to AIDS that may pull down populations down by pushing up death rates, including the environmental effects of population growth: deforestation, soil erosion and falling water tables.