Dorothy Detzer Denny, 87, a well-known pacifist who was executive secretary of the Women's International League for Peace and Freedom here for 23 years, died of congestive heart failure Jan. 7 in Monterey, Calif., where she had lived since 1969.

As Dorothy Detzer, she gained a worldwide reputation for her lobbying for peace. During her tenure as league secretary, she mobilized women for legislative action, helped bring about a congressional investigation of this country's munitions industry and was a key figure in getting the appointment of a woman to the U.S. delegation at the 1932 Geneva Disarmament Conference. She retired from the League in 1948.

Mrs. Denny was born in Fort Wayne, Ind. While still in her teens, she traveled on her own to the Far East and then went to Hull House in Chicago, where she had social service training under Jane Addams. After World War I, she went to Europe with the American Friends Service Committee, working in Austria and Russia.

In 1954, she married Ludwell H. Denny, foreign editor of the Scripps-Howard newspaper chain. They continued to live in Washington until 1969 but traveled widely. Mr. Denny died in 1970.

Mrs. Denny is survived by two stepdaughters, Diana Kalmus of Washington and Alice Robinson of Cambridge, England; a brother, Karl Detzer of Leland, Mich., seven grandchildren and eight great-grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society, or to a charity of one's choice.