WASHINGTON - Eugene V. Rostow, a law school dean who served in foreign policy positions for both Democratic and Republican presidents, died Monday of congestive heart failure at age 89.

Beginning in World War II and continuing through the Cold War, Rostow moved between the nation's universities and government service.

Rostow was undersecretary of state in the late 1960s when the nation's involvement in Vietnam was growing. He sought to establish breathing space for the South Vietnamese so they could govern themselves, his son, Victor, told The Washington Post.

At that same time his brother, Walt Rostow, was a special assistant to President Lyndon Johnson advocating military action in Vietnam.

Eugene Rostow was dean of the law school at Yale University from 1955 to 1965 and was credited with revamping the curriculum and elevating the school's reputation.

An adviser to the State Department in the early 1940s and again in the early 1960s, he became undersecretary of state for political affairs in 1966. He was head of the Arms Control and Disarmament Agency during the early part of President Reagan's administration.

Rostow was born in Brooklyn, N.Y., on Aug. 25, 1913, and reared in New Haven, Conn. He graduated from Yale in 1933 as a member of Phi Beta Kappa. He then studied economics at King's College, part of England's Cambridge University.

After returning to the United States he studied at Yale's law school, where he was editor of the Yale Law Journal. He practiced briefly with a major Wall Street law firm and then joined the Yale law faculty in 1938. He became a full professor six years later.

He took a leave of absence from Yale during World War II to serve in this country and abroad as an official of the Lend-Lease Administration, dealing with problems of providing supplies to America's allies.

In addition to his sons, Victor and Nicholas, survivors include his wife, the former Edna Greenberg, to whom he was married for 69 years, of Alexandria, Va.; a daughter, Jessica, of New Haven; two brothers, former National Security Adviser Walt Whitman Rostow of Austin and Ralph Emerson Rostow of Sarasota, Fla.; and six grandchildren.

Rostow's full name was Eugene Victor Debs Rostow, recalling the Socialist politician and presidential candidate Eugene V. Debs.