POCANTICO HILLS, N.Y. — LESTER BROWN says a deterioration in the world's food supply is no longer theoretical. As a result of malnutrition, infant mortality rates are already on the rise in Africa and South America. Mr. Brown is the director of Worldwatch Institute, a Washington think tank concerned with economic and environmental issues. He fears that the global food situation will worsen because of the huge reduction in global grain reserves.
``It leaves the world very vulnerable right now,'' he says. Another year of drought in the United States like that of 1988 could double or triple grain prices - ``no one knows how much. It would send shock waves through the world economy.'' It could lead to wider malnutrition and famine.
Brown was interviewed while attending a weekend conference of some 75 leaders in philanthropy at the 2,700-acre Rockefeller estate here to commemorate the 150th anniversary of the birth of John D. Rockefeller. One theme of the gathering was the role of philanthropic institutions in seeking solutions to third world poverty and the deterioration of the environment.
Brown lists many challenges. Forests are still being chopped down faster than they can grow. Deserts are growing. The ozone layer remains threatened. People are burning fossil fuels and forests at a rate that could cause the greenhouse effect. The number of plants and animals continues to diminish. Some 24 billion tons of topsoil are lost each year to wind and water - an amount equivalent to that covering all of Australia's wheat lands.
Brown and other members of his institute are now preparing the seventh annual edition of ``State of the World,'' a book-size report on the status of the world's population, food supply, environment, and other matters related to developing a sustainable world economy. Now published in 11 languages, it sells some 250,000 copies. Of these, 100,000 are in English. The report will also be the basis of a 10-part series to be aired on public television in the fall of 1990.
``I keep hoping to offer an upbeat report,'' he says. ``But we are not close to that yet.''
Brown finds ``disturbing'' the effect of environmental degradation - pollution, flooding, waterlogging, salting of irrigation systems, as well as the loss of topsoil - on agriculture.
``These negative factors are beginning to offset the positive effects of the technological revolution in agriculture,'' he says. ``There has been a dramatic slowdown in world food output growth in the late 1980s.''
At the same time, world population continues its rapid growth, adding 840 million people in the 1980s to reach 5.2 billion. Population growth in the 1990s could reach 960 million.
``The world's farmers are trying to feed an extra 88 million people each year,'' he says.
The World Bank has a study of Africa underway which, as one possibility, extrapolates into the next century present trends in that continent regarding food production, environmental damage, and population growth. It's called the ``nightmare scenario,'' notes Brown.
In the US, the normal grain crop runs around 300 million tons and domestic consumption about 200 million. The remainder is exported or held in reserve. However, in 1988, because of the drought, production came only to 196 million tons. Domestic consumption in the year since then will amount to about 206 million tons - a shortfall of 10 million tons. In addition, exports are expected to reach around 100 million tons this year.
US grain reserves fell 100 million tons last year and should drop another 18 million tons this year, according to the US Department of Agriculture. ``Everyone is keeping their fingers crossed that we are somehow able to rebuild world food stocks,'' he says.
Brown warns that the water table is falling in the Great Plains of the Southeast US and in the north plains of China, factors that could trim crop yields.
On the positive side, the US has set aside some 35 million acres of land less suitable for farming for conversion to grass lands or forests. This set-aside, equal to 10 percent of total crop land in the US, has greatly reduced soil losses in the US, Brown says.
Brown hopes that the easing of East-West tensions will release sufficient resources from the military to deal more adequately with the world's problems of poverty and environmental degredation. ``It might set the stage for a major reordering of priorities,'' he says.