A brief Pentagon statement announcing the resignation gave no reason for White's decision. In the statement, Rumsfeld thanked White for his service and said that his departure date had not yet been determined.
White became engaged in a public dispute with Rumsfeld last year over the defense secretary's proposal to cancel the Crusader artillery project, which White said was vital to the Army's future. Rumsfeld decided it was not suited for wars of the future and eventually canceled the program.
White also became embroiled in a controversy over his former role as an executive with Enron Corp., the scandal-ridden energy trading company.
Speculation that White would leave his post has circulated widely for many months, but there appeared to be no recent event or conflict that prompted him to submit his resignation on Friday, one senior official said.
White is a Vietnam veteran and former Special Forces soldier. He became Army secretary on May 31, 2001.
The Army secretary's responsibilities by law are for all matters relating to Army personnel, reserve affairs, installations, environmental issues, weapons systems development and financial management.
None of the three service secretaries is in the military chain of command.
White is a West Point graduate, class of 1967. He rose to the rank of brigadier general before retiring from the Army in July 1990.
From 1990 to 2001 White was employed by Enron and held several senior executive positions.