Nat Weinberg, 71, a labor economist and retired director of special projects and economic analysis for the United Auto Workers union, died May 19 of cardiac arrest at Sibley Memorial Hospital.

Mr. Weinberg, a resident of Bethesda, moved to the Washington area upon his retirement from the UAW in 1974 and since then had been a consultant to several organizations, including the United Mine Workers, the House Interior and Insular Affairs Committee and the Labor Department. For the past two years he had been an adviser to the United Nations Commission on Transnational Corporations.

He spent most of his working life with the UAW in Detroit and was instrumental in the union's successful negotiation of employer-financed pensions and supplemental unemployment benefits. Since joining the union staff in 1947 he had participated in all major negotiations with the auto industry and he also worked on income and pension guarantees for workers displaced by imports.

Mr. Weinberg was born in New York City. He attended Brookwood Labor College in Katonah, N.Y., and graduated from New York University. He was in the research department of the International Ladies Garment Workers Union until 1944, when he moved to Washington and went to work for the Labor Department. He remained here until joining the UAW in Detroit.

He had been a visiting lecturer at several universities, including the University of California at Berkeley, Davis, and Santa Cruz, and Cornell University, and he had served on several governmental and academic commissions, including the Michigan Governor's Study Commission on Automation and the Harvard Overseers' Committee to Visit the Department of Economics.

He was a member of the NAACP, Americans for Democratic Action and the American Civil Liberties Union.

Survivors include his wife, Ruth, of Bethesda; two sons, Robert, of Washington, and Larry, of Arlington; a brother, Joseph, of Flushing, N.Y., and five grandchildren.