Betty Southard Murphy, a trial lawyer who became chairwoman of the National Labor Relations Board and the first woman to serve on the board, died on Oct. 16 in Washington. She was 77.

The cause was pneumonia, said David Grant, a partner at the Washington law firm Baker & Hostetler, where Mrs. Murphy had been a partner since 1980. She lived in Alexandria, Va.

When Mrs. Murphy was sworn in as a member and chairwoman of the labor board in February 1975, President Gerald R. Ford said he had appointed her “not because she was a woman” but because she was “the most qualified and best respected person.” The board is responsible for safeguarding workers’ organizing rights and preventing unfair labor practices.

By then, Mrs. Murphy had already served as administrator of the Wage and Hours Division of the Department of Labor, which enforces federal laws regarding minimum wages, overtime pay, child labor and migrant labor, among other employment issues.