PHILADELPHIA - Barbara Gittings, 75, a gay rights activist since the late 1950s, died today after a lengthy fight with breast cancer, according to Mark Segal, a friend and the publisher of the Philadelphia Gay News.

Ms. Gittings helped organize the New York City chapter of the Daughters of Bilitis, an early lesbian rights organization, in the 1950s. During her work with that group, she met her life partner, Kay Lahausen. Ms. Gittings edited the group's publication, The Ladder, from 1963 to 1966, and worked with Lahausen on her 1973 book, "The Gay Crusaders."

She first became well-known to the public in 1965, when she helped organize gay-rights demonstrations at the White House and Independence Hall. In 2005, she and Lahausen attended the unveiling of a state historic marker noting those demonstrations across the street from Independence Hall.

Ms. Gittings had served as head of the American Library Association's Gay Task Force; in 2003, the association presented her its highest honor, a lifetime membership.

Ms. Gittings was also active in the campaign that led to the American Psychiatric Association's 1973 decision to drop homosexuality from its list of mental disorders.

She and Lahausen lived in Philadelphia and Wilmington in their later years; they recently moved to an assisted living center in Kennett Square, where Ms. Gittings fell into a coma this morning and died this evening, Segal said.

In addition to Lahausen, Ms. Gittings is survived by her sister, Eleanor Gittings Taylor.

Funeral arrangements were incomplete.