Dr. Euphemia Lofton Haynes, 90, a former D.C. board of education president and member and a Washington educator for nearly 50 years, died Thursday at the Washington Hospital Center. She had been hospitalized since suffering a stroke July 25.

Dr. Haynes served as school board president from July 1966 to July 1967. A fourth-generation Washingtonian, she was a product of the same school system that she later headed.

She served as a member of the old nine-member school board, then appointed by judges of the U.S. District Court for the District of Columbia, for seven years before becoming its president.

During that time she was an active and outspoken critic of the school system's de facto structure of segregation and its "track system," which placed students in academic or vocational programs depending on ability.

The track system, which had structured the city's schools for a number of years and which was said to discriminate against black and poor students, was abolished along with de facto segreagation by Judge J. Skelly Wright in June 1967, when Mrs. Haynes was board president.

Mrs. Haynes had favored black civil rights leader Julius W. Hobson's suit, charging the scchool system with racial and economic discrimination, which led to Judge Wright's decision.

She also was school board president when the machinery for an election to establish collective bargaining rights for public school teachers was set up in March 1967. She left the board in 1968 when the city's first elected school board took office.

Mrs. Haynes graduated from Smith College in 1914. She earned a master's degree in education from the University of Chicago and a doctorate in mathematics from Catholic University.

She taught mathematics in Washington high schools and, in 1930, established a methematics department at old Miners Teachers College here. She was professor and chairman of the department when she retired in 1959.

After retiring, Mrs. Haynes became active in Catholic organizations. She was president of the Washington Archdiocesan Council of Catholic Women from 1964 to 1966. She also served on the board of Catholic Charities and as member of the D.C. branch of the National Conference of Christians and Jews.

In 1959, she received the Papal medal, "Pro Ecclesia et Pontifex" for her service to the church and her community.

Her husband, Dr. Harold A. Haynes, a former deputy superintendent of the city's public schools, died two years ago.

Mrs. Haynes leaves no immediate survivors.