Howard G. Gamser, 64, a former member and chairman of the National Mediation Board and an authority on labor law and arbitration, died of pneumonia April 20 at George Washington University Hospital.

Mr. Gamser, who lived in Washington, was born in New York City. He earned a bachelor's degree at the City College of New York, a master's degree at Columbia University and a law degree at New York University. He was a captain in the Army in World War II.

From 1946 to 1952, he was a lawyer with the National Labor Relations Board in Washington. He then returned to New York, where he worked for the Wage Stabilization Board and the New York State Board of Mediation.

In 1961, he came back here as chief counsel of the House Education and Labor Committee. He was appointed to the National Mediation Board in 1963 and served it as a member and chairman until 1968.

Since then, Mr. Gamser had conducted a private practice in arbitration. In the course of it, he served on a number of official bodies, including the Federal Service Impasses Panel, of which he was chairman from 1977 to 1982. The panel was established in 1970 to help resolve high-level disputes between government agencies and unions.

He had been chairman of the Foreign Service Impasses Panel since 1981 and was chairman of the grievance committee of the International Monetary Fund.

He lectured on labor law at the London School of Economics and Georgetown and Columbia universities. He was the author of a number of papers published in professional journals.

Mr. Gamser was a director of the American Arbitration Association and a member of the National Academy of Arbitrators, the Industrial Relations Research Association and the D.C. and Federal bar associations.

Survivors include his wife, Doris P., of Washington; a daughter, Diana, a student at the London School of Economics; a son, Matthew S., an official of the Agency for International Development in Khartoum, Sudan, and his mother, Rose, and a brother, Robert, both of New York City.