Intended for policymakers, this document focuses on environmental factors limiting the expansion of the world's food supply, the dilemma of fostering third world economic development, and prospects for energy development. The first of five parts gives an overview of a 1983 Population Reference Bureau conference which focused on current thinking about population, resources, and environmental issues. The second part examines current population growth and efforts to curb world population increase. Countries at zero population growth are listed and tables show absolute increases in world population, slowly growing countries, and regions and countries where families average five or more children. The next part discusses short term (technical, political, and social) and long-term obstacles (soil erosion, misuse of irrigation, and altering natural ecosystems) to feeding future populations. The fourth part addresses ecological, economic, and social implications of using fossil fuels in third world countries and explains ways in which the use of fossil fuels can lead to a higher gross national product (GNP) and a corresponding increase in Physical Quality of Life Index (PQLI). Figures showing relationships between GNP, birthrates, and PQLI are given. The final section, policy choices, concludes that curbing population growth is the most important element of bringing about a sustainable world. (LH)