Map,,Richard Furno; Map,,Brad Wye CAPTION:INCOME AND THE ENVIRONMENT Wealthy, industrialized nations of the North generally view the Earth Summit, which begins Wednesday in Rio de Janeiro, as an opportunity to address environmental problems of international scope, such as global warming. Less wealthy countries, however, will arrive with somewhat different agendas that emphasize their quest of economic development. Especially in the southern hemisphere, people who cannot afford the barest necessities are understandably less interested in ecology than in achieving adequate living standards. Many less-developed nations expect wealthy countries to provide development aid, grants and debt relief in exchange for such environmental measures as preservation of rain forests. These demands come at a time when the income disparity between rich and poor nations is growing. According to United Nations studies, 23 percent of the planet's people, most of whom live in developed nations, receive 85 percent of all income. According to the United Nations: Approximately 4.2 billion people live in the developing world, about 1 billion of them in poverty. Two-thirds of all the Earth's poor are less than 15 years old. Of the world's 1 billion poor, 450 million live in areas with "low potential" for agricultural use; 450 million dwell in "ecologically vulnerable" regions prone to flood, soil erosion and similar problems; and 100 million live in urban slums. Sixty-five percent of the population of sub-Saharan Africa lives in poverty, as do 35 percent of those in Latin America, 28 percent of people in the Middle East-North Africa, and 25 percent of Asians. In 1990, external debt of developing nations was estimated at $1.3 trillion. People living in industrialized nations consume 48 to 72 percent of the world supply of basic food commodities, including milk, meat and cereals. CAPTION: WORLD POPULATION TRENDS One of the world's most compelling environmental issues will receive only minimal attention at the Earth Summit: population growth. Yet the United Nations recently announced new projections indicating that global population will reach 11.6 billion by 2150 - more than double the present figure of 5.4 billion. At least 90 percent of that growth is expected to take place in the developing nations of the so-called Third World, where fertility rates (the number of children per mother) have been averaging around 4. By contrast, the average rate in developed countries is about 1.9 children per woman. Every 60 seconds, according to the Population Reference Bureau, a nonprofit research organization in Washington D.C., 236 children are born in less-developed countries, the corresponding figures are 33 born and 22 dying. At that rate, the world will add between 90 to 100 million people per year during the 1990s, PRB estimates. There is little doubt that relentless increases in population will have significant effects on the environment. Earth Summit Secretary General Maurice Strong has said that "the relationship between population dynamics an the ecosystems of which the survival and well being of people depend is decisive in achieving sustainable development."