Juanita Duggan Roberts, 70, a principal secretary and confidant of Lyndon B. Johnson during his years as president, and who was one of the first officers of the Women's Army Corps to be promoted to colonel, died of cancer May 26 at Emory University Hospital in Atlanta.

Col. Roberts had known Johnson since 1938 and became a member of his congressional staff in 1953. She remained close to Johnson after he left office. She was one of the key organizers of the LBJ Presidential Library at the University of Texas.

Friends remember her as a "quiet, competent secretary" who managed the mundane tasks of her office well. The president sometimes called her "Miss Efficiency," and called on her often to handle sensitive and touchy situations for him behind the scenes.

At the end of the Johnson administration, Col. Roberts became a staff officer in the Pentagon headquarters of the Joint Chiefs of Staff. She lived at the Watergate Hotel and spent much of her time attending to chores involved in running the LBJ Library. She was a member of the library's board of directors at the time of her death.

Col. Roberts was born in Port Arthur, Tex., and graduated from Texas Woman's University in 1933. Five years later she married H. Ray Roberts, who later was a Democratic congressman from Texas. They were divorced in 1946.

During the 1930s, she worked as a home economist at Texas A&M University and was president and general manager of Holiday House, a tea room in Port Arthur.

She served on active Army duty from 1942 until 1946. Her decorations included the Legion of Merit. When Johnson became vice president in 1961, she was placed back on active duty and promoted to colonel. She retired in the 1970s.

She leaves no immediate survivors.