Donald D. Webster, 74, an insurance company executive who had been active in aviation here, died Wednesday after suffering a heart attack while visiting friends in Washington.

He lived in Bethesda, where he operated the Donald Webster Insurance Agency, which he had established in 1968. Before that he had owned the Aero Insurance Agency for 20 years.

A pilot before World War II, Mr. Webster left his Washington insurance business to serve during the war as an intelligence officer with the Army Air Forces in Europe.

After the war, he was Washington branch manager of Aero Insurance Underwriters until setting up his own company, Aero Insurance Agency.

Mr. Webster was a former president of the National Aeronautic Association, the Aero Club of Washington and the Washington Aviation Club and was a charter member and former treasurer of the National Pilots Association.

He had served as president and director of Pilgrim Helicopter Services Inc. during the early 1960s. He has been a member of the national board of the Civil Air Patrol and commander of the National Capital Wing of the CAP. He also had been a member of the Washington Air Derby Association and the Quiet Birdmen.

Mr. Webster was born in Chicago and came here with his family as a child. He was a graduate of Randolph Macon Academy in Front Royal, Va., and attended George Washington University.

He had been an official of Marjorie Webster Junior College, which was founded by his sister, Marjorie Webster, who died in 1963.

He is survived by two sons, Michael, of Newcastle, Maine, and Donald, of North Conway, N.H.; a daughter, Marjorie Wessels, of Detroit, and nine grandchildren.