Marion Moncure Duncan, 64, a former national president general of the Daughters of the American Revolution and member of the Board of Visitors of the College of William and Mary, died of cancer Saturday at the Circle Terrace Hospital, Alexandria.

Mrs. Duncan also was an insurance agent and managed the insurance department of her husband's business, Bob Duncan Real Estate-Insurance, from about 1960 until her retirement two years ago. She was a member of the Virginia Association of Insurance Agents.

A lifelong resident of Alexandria, Mrs. Duncan attended public schools there, the College of William and Mary and George Washington University. In 1966 and 1970 she was appointed to the four-year terms for the William and Mary Board of Visitors.

From 1962 until 1965, Mrs. Duncan served as president general of the national society of the DAR. Besides her work in the DAR. Mrs. Duncan's interest in history and historic preservation led her to be active in the Alexandria Bicentennial Commission, the Colonial Dames of America and the Order of Fisrt Families of Virginia. She also was a member of the Jamestown Corp. and co-authored a 40-generation genealogical study of her family, which was published in 1968.

Mrs. Duncan received awards from the Boy Scouts of America, the Sons of the American Revolution and Soroptimists International.

In 1963, she served on the Distinguished Awards jury for the Freedoms Foundation and received the George Washington Medallion award in 1964 "for outstanding achievement in bringing about a better understanding of the American Way of LIfe."

Mrs. Duncan is survived by her husband Robert, of the home in Alexandria; and three sons, Robinson M. of Leesburg, and Moncure, and Bruce Grigg, both of Alexandria; a sister, Mrs. Clyde C. Lamond of Alexandria, a brother, Thomas Moncure, also of Alexandria, and four grandchildren.