Robert F. Pfeiffer, 51, a State Department Foreign Service officer who specialized in Asian affairs, died Monday at Northern Virginia Doctor's Hospital in Arlington after a heart attack.

Mr. Pfeiffer joined the State Department in 1958. After Japanese language training, he was assigned to Tokyo and Fukuoka, Japan, where he served through the 1960s. In the early 1970s, he was assigned to Paris and Geneva as a labor attache.

In the late 1970s, he was assigned to the State Department here and was the regional labor adviser in the Bureau of East Asian and Pacific Affairs at the time of his death.

In 1977, he received the State Department's Superior Achievement award.

Mr. Pfeiffer, who was born in Brooklyn, graduated from Harvard College in 1951. He then served with the Army in the Far East as an intelligence officer from 1952 to 1956.

He was a member of the Washington Harvard Club and was active in the American Foreign Service Organization.

Survivors include his wife, Setsuko; a son, Francis, and a daughter, Mari, all of Falls Church, and his mother, Frances, of New York City.

The family suggests that expressions of sympathy be in the form of contributions to Harvard College, Cambridge, Mass.