Barbara M. Watson, 64, a former ambassador to Malaysia and assistant secretary of State for consular affairs, died of pneumonia Feb. 17 at George Washington University Hospital.

Miss Watson, who lived in Washington, joined State in 1966 as deputy administrator in the Bureau of Security and Consular Affairs. In 1968, she was named administrator of the bureau with the rank of assistant secretary of State.

Except for the years 1975 to 1977, when she practiced law in Washington, she continued this work until 1980.

She was appointed ambassador to Malaysia in that year and served there until 1981.

Since resigning, she had practiced law in Washington. She also was a senior associate of von Kloberg & Associates, international consultants.

Miss Watson was born in New York City. She graduated from Barnard College and earned a law degree at New York Law School. She was an attorney with New York City from 1962 to 1964, when she was appointed executive director of the New York City Commission to the United Nations.

She received honorary doctorates from the University of Maryland and Mount St. Mary's College. In 1974, she received the State Department's Luther I. Replogle Award for Outstanding Management in Foreign Affairs.

Miss Watson was a member of the boards of Fordham University, Barnard College, the Georgetown University School of Foreign Service, the Georgetown Center for Strategic and International Studies, Radio Liberty/Radio Free Europe, and the Wolf Trap Foundation for the Performing Arts.

Survivors include two brothers, Douglas C. Watson and Judge Samuel Watson, both of New York, and a sister, Grace Elizabeth Watson of Washington.