ROBERT G. GILPIN, professor emeritus of politics and international affairs, died June 20 in Waterbury, Vt. He was 87. Gilpin joined the faculty in 1962 and taught for 36 years. He was an expert on international political economy, and his early studies examined the role of scientists in the formation of policy and the impact of nuclear weapons in international relations. Among his books was The Political Economy of International Relations, which won the 1988 Woodrow Wilson Foundation Book Award for the best book in political science.