Mott, pioneer in women's rights; Valiant Friend: The Life of Lucretia Mott, by Margaret Hope Bacon. New York: Walker & Co. 265 pp. $8.95.

Lucretia Mott, a Quaker, became one of the leading figures in the American reform movement a century ago. As a young woman she developed her considerable talents and became convinced of her mission to right the wrongs around her. Her husband, James Mott, shared her views and life in a marriage partnership that sustained all of her efforts.

This is a biography of achievement, a straightforward record of years of determination to follow the ''light within,'' in spite of disapproval of some members of the Society of Friends and actual harassment of anti-abolitionists, Tammany toughs, and hostile Philadelphia mobs. As years passed, gains were made: slavery was abolished; women joined the professions; and the movement begun at Seneca Falls became the National Woman Suffrage Association.