Sandra B. O'Leary, 50, a senior economic adviser to three secretaries of state and a former deputy assistant secretary of state for economic policy in the State Department's bureau of East Asian and Pacific affairs, died of cancer Aug. 9 at her home in McLean.

Dr. O'Leary began her federal career in 1979 in the office of the U.S. Trade Representative. Later she served in the Treasury Department and the Department of Commerce.

She joined the State Department in 1986 as the senior economist on the policy planning staff of Secretary of State George Shultz. In this role, she analyzed the implications of globalization for American foreign policy. When James Baker was secretary, she conceptualized and coordinated efforts to aid economies in transition from communism to market-based systems.

From 1990 to 1995, Dr. O'Leary was director of the planning and economic analysis staff of the State Department's bureau of economic and business affairs. She was a coordinator of efforts to secure international financial support for U.S.-led coalition operations during the Persian Gulf crisis. She also worked on economic policies for the Middle East in the post-Gulf War period.

In 1995 and 1996, she was deputy assistant secretary of state for economic policy in the bureau of East Asian and Pacific affairs under secretary Warren Christopher. In that role she worked on economic cooperation for the region.

Dr. O'Leary's most recent positions included professorships at the Foreign Service Institute and the National Defense University.

She was born in Hackensack, N.J., and graduated from Smith College. She received a master's degree in international relations at the Johns Hopkins School of Advanced International Studies and a doctorate in political science at Johns Hopkins University.

She was a member of Immanuel Presbyterian Church in McLean.

Survivors include her husband, James O'Leary, and two daughters, Glynis and Abigail, all of McLean; her father, Boniface Brazaitis, and a sister, C.B. Lovell, both of Columbia.