Pitman Benjamin Potter, 89, an authority on international affairs who retired in 1957 as dean of the graduate school of American University, died Friday at his home in Washington after a stroke.

He joined the faculty of American University in 1944 as Grozier professor of international law and chairman of the department of international relations and organization, and became dean of the graduate school in 1947.

Dr. Potter was born in Long Branch, N.J. He earned his bachelor's, master's and doctoral degrees at Harvard University. He taught political science at the University of Wisconsin and was a professor at the universities of Chicago, Texas, California and Delhi, India, as well as at Harvard.

He was professor of international organization at the Graduate Institute of International Studies in Geneva, Switzerland, from 1932 to 1941 and chairman of the political science department at Oberlin College before coming to American University.

Dr. Potter had been managing editor of the American Journal of International Law during 1943-48, and had served on its board of editors since 1925. He was a former officer of the American Society of International Law. In 1935, he was a legal adviser to the Ethiopian government as part of an effort of the League of Nations to settle the dispute between Ethiopia and Italy.

He was the author or coauthor of numerous books and articles in his field. He belonged to Phi Beta Kappa, the American Political Science Association, the American Society of Public Administration and the Cosmos Club.

His first wife, the former Jessie Isabelle Dalton, died in 1940.

Survivors include his wife, the former Margaret Ruth Hardy, of Washington; two sons by his first marriage, Dalton, of Bethesda, and James Lane, of Canton Center, Conn.; two children by his second marriage, Charles Benjamin, of New York City, and Louisa P. Wellemeyer of Alexandria, and nine grandchildren.