Edna Frazier-Cromwell, 50, a civic activist who since 1983 had been a member of the D.C. school board, where she became known for her advocacy of competency testing for teachers, died of cancer yesterday at her home in Washington.

She was appointed to the board in 1983 to succeed Frank Smith Jr., who had resigned to take a seat in the D.C. City Council. In November 1983 Mrs. Frazier-Cromwell won election to the Board in her own right.

During her years on the board, she championed programs to fight drug abuse and was an outspoken opponent of granting tuition tax credits to private elementary and secondary schools. Although she had cancer for the past two years, she continued to attend board meetings regularly.

Mrs. Frazier-Cromwell chaired the committee that last month passed a resolution requiring new D.C. public school teachers to pass competency tests. She also was instrumental in enacting legislation to bring updated standardized tests to public school students.

Mrs. Frazier-Cromwell represented Ward 1, an area of about 80,000 persons where income levels, despite pockets of affluence, are among the lowest in the city. She won election to the board with the support of Mayor Marion Barry, council member Frank Smith Jr. and the Washington Teachers Union.

Before joining the board, she served as chairman of the 14th and U Streets Coalition, an organization that represented 30 community groups in Ward 1, and as an Advisory Neighborhood Commissioner.

Mrs. Frazier-Cromwell was born in Knoxville, Tenn., and moved to Washington in the early 1950s. She was a graduate of Dunbar High School. In 1959 she earned a bachelor's degree in economics and political science at Howard University.

From 1959 to 1961 she was a camp counselor with the D.C. Recreation Department. From 1962 to 1969 she worked for the Library of Congress, where she became a legislative researcher. She then joined the Congressional Quarterly, where she was a senior researcher and library information director before leaving in 1983.

Survivors include her husband, Oliver Cromwell, and a stepson, Michael Cromwell, both of Washington, and her mother, Velma Frazier of Knoxville, Tenn.