Marianne S. Karydes, 49, a member of the executive committee of Arlingtonians for a Better County, a civic group, and a former vice chairman of the Arlington County Democratic Committee, died of a heart attack Feb. 2 at Arlington Hospital.

Mrs. Karydes took part in a wide range of civic and school activities in Arlington, including desegregation and other school matters, consumer questions and television. She was a member of the county manpower commission, the economic development commission, the youth commission and the task force on drug problems.

In the early 1970s, she was president of the Positive Action Committee on Education, a group that advocated busing some white children to the Drew Elementary School rather than placing the full burden for desegregation on the school's black students.

In the same period, she helped found Woodlawn High, Arlington's alternative high school. It is now the H.B. Woodlawn Secondary School and is so highly regarded that it has a waiting list.

Mrs. Karydes played a major role in persuading the Arlington School Board to set up a human relations department.

At a school board meeting last night, Chairman Evelyn Reid Syphax recalled Mrs. Karydes as one of the community's outstanding citizens. "As an advocate of quality education in our public schools, Mrs. Karydes demonstrated her dedication through extensive volunteer service," Syphax said.

Mrs. Karydes was a director of the Community Access Corp., a citizens group which is to take over the public access station in the Arlington cable television system. She also was a member of the NAACP and the Woman's National Democratic Club. She wrote a column for the Arlington News.

Mrs. Karydes, who lived in Arlington, was born in Lakewood, N.J. She grew up in Staunton, Va., and graduated from Mary Washington College in Fredericksburg, Va. She moved to the Washington area in 1953 and worked for the CIA for about three years. From 1975 until 1978, she worked in the Office of Telecommunications Policy in the Commerce Department. She then joined the Federal Communications Commission, where she was involved in consumer affairs. She resigned in 1982 to become a communications consultant.

Survivors include her husband, George Karydes, of Arlington; a daughter, Terry Jeanne, of Hoboken, N.J.; two sons, Andrew George and William Stivers, both of Arlington; two sisters, Patricia S. Bauer of Fort Washington, Md., and Julia S. Collins of Wilton, N.H., and a brother, John R. Stivers of Arlington.