David Ord Alexander, 50, a coal utilization specialist in the Department of Energy's fuel conversion analysis branch, died Friday at his home in Washington after a heart attack.

He had joined the government as a coal industry expert and coal consultant with the Old Federal Energy Office in April 1974. He joined the Energy Department when it was established in October 1977.

Mr. Alexander was native of Washington and attended both the U.S. Naval Academy at Annapolis and George Washington University.

During the early 1950s, he was a field project engineer for the T. W. McGuire Company. From 1954 to 1960, he worked for the National Coal Association as fuels utilization and conversion specialist, as a government relations officer, and as an assisstant engineering director.

He was an associate parner of two consulting engineering firms, then founded and served as president of the old Nautical Industries Corporation in 1968.

Nautical industries designed and manfuactured underwater diving equipment and conducted undersea studies for government and private organizations. It was disbanded before Mr. Alexander joined the government. o

He was a member of the National Press Club, the Naval Academy Alumni Association, and the Washington Canoe Club. He was a charter member of Cedam International, a conservation organization, and had been and Eastern director of Trout Unlimited.

Survivors include his wife, Jocelyn Arundel Alexander, two daughters, Ann Russel Cresap and Jocelyn Lee, a son, Russell Ord, and his mother, Vida Ord Alexander, all of Washington.