Mildred Foster Gaines, 76, retired chairwoman of the riding department at The Madeira School and a noted horsewoman in Northern Virginia, died of a stroke March 25 at her home in Leesburg.

Miss Gaines retired in 1979 after 39 years as chairwoman of the riding department at Madeira. Gaines Hall, the indoor riding facility at the school, is named in her honor. In retirement she had taught riding at her farm near Leesburg.

She was a founder of the Virginia School and College Riding Association and of the Warrenton Pony Show. From 1945 to 1979 she owned and operated the Greenway Equitation School near Great Falls.

Miss Gaines also was a judge of the American Horse Show Association and a member of the Warrenton, Fairfax and Loudoun hunts.

In the 1920s and 1930s her horses competed in point-to-point races and in competitions on the Virginia horse show circuit.

In 1978 Miss Gaines was named Citizen of the Year by the McLean Business and Professional Club for her contributions to the community, including 34 years as an officer of the McLean Horse Show Association and service as a first aid instructor for the McLean Volunteer Fire Department.

A native of Warrenton, Miss Gaines attended Southern Seminary Junior College.

She is survived by a brother, John Gaines of Amissville, Va.