Margaret Cunningham Rush, 65, retired assistant to the director of the Georgetown University Hospital dental clinic and a lifelong area resident, died Wednesday of heart disease at her home in Kensington.

Mrs. Rush, who recently moved to Kensington, was born in Washington and was a graduate of Holy Trinity High School. In the late 1930s, she worked as a secretary in the office of the registrar at Georgetown University Medical School.

In 1942, she married Dr. Robert Cornelius Rush. Dr. Rush died in 1969.

She returned to Georgetown University in 1970 and worked first as a secretary for the dean of the Dental School and later as assistant to the director of the dental clinic. She retired for reasons of health in 1980.

Mrs. Rush was a member of the Shrine of the Most Blessed Sacrament Catholic Church and was active in church organizations. She was a former member of the Congressional Country Club.

Survivors include three daughters, Judith Ryan of Arlington, Margaret Roddy of Silver Spring and Mary Delia Rush of Kensington; a son, Army Lt. Robert C. Rush Jr. of Hinesville, Ga.; a sister, Ann Elizabeth Breen of Washington, and a brother, George Cunningham of Powells Point, N.C.