Ben D. Segal, 66, a former special labor assistant to Mayor Walter E. Washington and a longtime advocate of equal employment opportunity and other civil rights causes, died June 4 at George Washington University Hospital following a heart attack.

Mr. Segal spent his life working for fair treatment of minority groups in the market place, in public accommodations, in housing, in education, at the polls and, most particularly, in the matter of jobs.

He joined Mayor Washington's staff in 1968 and remained on it until 1978, when he resigned. As the city's special assistant for labor-management affairs, he gained a reputation for quiet effectiveness in disputes involving a wide range of employes, from nurses to firemen.

The list of organizations for which he worked is almost as numerous as the goals he sought. In the late 1940s, he was the education director of the Textile Workers Union of America, working in the South. He then became associate director of education for the Congress of Industrial Organizations, now part of the AFL-CIO. In 1953, he took a Fullbright Fellowship to study the British Labor Party.

When he returned to this country, he joined The Fund for the Republic, where he was trade union consultant and director of the trade union program on civil liberties and civil rights. In the late 1950s, he was named education director of the International Union of Electrical, Radio and Machine Workers.

He later served on the President's Council on Equal Opportunity and in 1965 he went to work for the Equal Employment Opportunity Commission as director of the Office of Liaison. He was chairman of the Community Advisers on Equal Employment when he joined the Washington administration.

Mr. Segal said in an interview in 1967 that the city had made "amazing progress" towards equal treatment of blacks since he moved here in the early 1950s. He recalled that one of the safeguards against embarrassment when he first came here was a sandwich in his briefcase. The sandwich meant that he and his black friends could have lunch together in the still largely segregated city.

"There were only one or two public places I could eat with my Negro friends," he said. "Once in a while we'd sit at a drug store counter--but nobody would serve us."

After leaving the District Building, Mr. Segal went to work for the Labor Department, where he was a wage analyst in the Division of Wages and Hours at the time of his death.

Mr. Segal was born in Hungary and grew up in Chicago, where his family moved when he was 9. He graduated from the Central YMCA, now Roosevelt University, and took graduate courses at the University of Chicago. He was a conscientious objector during World War II.

He was a member of the board of Friendship House in Southeast Washington and a founder of VOICE, a citizens group. He was an outspoken supporter of home rule for the District of Columbia. He taught at American University and at his death was teaching a course called "Quality of Worklife" at the University of the District of Columbia.

Survivors include his wife, Elizabeth of Washington; three daughters, Barbara of Washington, Margery of New York, and Doris Segal-Matsunaga of Honolulu, Hawaii, and three sisters, Lillian Yarmat and Esther Klowden, both of Chicago, and Eva Emeric of Cincinnati.