Mildred Chaffin Portner, 68, secretary of the Library of Congress for 23 years before retiring in 1969, died of cancer Tuesday in a Saint Petersburg, Fla., hospital. She had moved to Florida six years ago.

During her years as the library secretary, Mrs Portner won awards for helping develop management systems that were adopted by congressional offices and for her work in training staff personnel.

She helped reorganize the office of then Senate majority leader Lyndon B. Johnson, and later helped plan the Lyndon B. Johnson Memorial Library in Austin, Tex.

She was a member of the Society of American Archivists, the Society of Personnel Administration, the Capitol Hill Association, and the D.C. Library Association. She also belonged to the International and Michigan State clubs.

Mrs Portner, was a native of Ithaca, Mich., and a graduate of the University of Michigan. She worked for the Michigan state government, as personnel director of a Detroit department store, and for the old Works Progress Administration in Michigan before coming to Washington in the 1940s. She joined the Library of Congress in 1946.

Survivors include her husband, Dr. Stuart Portner, of the home in Saint Petersburg, and one grandchild. A son, James, died in 1965.

The family suggests that expressions of sympathy by in the form of contributions to the American Cancer Society, or to the Scholarship Fund, Friends of the Lyndon B. Johnson Library, 2213 Red River, Austin, Tex., 78705.