Marion Tully Dimick, 77, a resident of Washington since 1926 who had served on the boards of cultural and financial institutions here and who was known for her quiet but substantial contributions to charity, died at her home Tuesday after a heart attack.

Mrs. Dimick had served as vice chairwoman of the board of the National Symphony. She also had served on the boards of the Potomac School, the Washington Opera Society, the Washington Home, the Wolf Trap Associates and the women's board of Children's Hospital. She had been a member of the board of the National Savings & Trust Co.

Mrs. Dimick was a member of Christ Episcopal Church in Georgetown and the Sulgrave Club.

She donated substantial time and money to organizations ranging from churches and hospitals to the symphony.

Mrs. Dimick was born in Corning, N.Y., reared in Locust Valley, N.Y., and came to Washington after marrying Reeve Hoover. That marriage ended in divorce.

During World War II, she served as a Red Cross volunteer in Washington. In 1951, she married John Dimick, an archeologist, and accompanied him on expeditions to Egypt and Guatemala.

In addition to her husband, of Washington, Mrs. Dimmick's survivors include four children by her first marriage, William G. Hoover of Dallas, Louise Neuhoff of Washington, Hilary Luther of Villanova, Pa., and Clara Hendin, of Randolph Center, Vt.; a sister, Alice Tully of New York City; 13 grandchildren; and one great-grandchild.

The family suggests that expressions of sympathy be in the form of contributions to Children's Hospital National Medical Center, Washington, D.C.