A brief Pentagon statement late Friday announcing the resignation, which came from Rumsfeld's office, gave no reason for White's departure. He made no public comment, and Rumsfeld left early Saturday for the Persian Gulf area.
On Saturday, the official, who spoke privately with White, said Rumsfeld had asked him to resign. Speaking on condition of anonymity, the official said no single event or conflict precipitated the firing. Rumsfeld told White he wanted to steer the Army in a new direction.
Army officials said White had no public comment.
"Under the circumstances, the most dignified thing to do is to say nothing and accept Secretary Rumsfeld's decision as gracefully as possible," said Charles Krohn, a spokesman for White.
In his brief written statement Friday, Rumsfeld tersely thanked White for his "long and able service to the country." He said White's departure date had not yet been determined.
White's departure portends a major shake-up in Army leadership. The top uniformed officer, Gen. Eric Shinseki, is due to finish his term as Army chief of staff in June. President Bush has not nominated a successor.
Speculation that White would quit has circulated widely for many months, but there appeared to be no recent event or conflict that prompted him to do so, said a senior official, speaking on condition of anonymity.
White, 59, 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.
That was one of several areas of tension between Army leaders and Rumsfeld, who also has questioned the service's plans to invest in the Stryker, a wheeled combat vehicle that is a prototype replacement for the tank.
The Army had considered the Crusader a key to its strategy for modernizing U.S. land forces and transforming them to a lighter, more mobile force. The Crusader was a 155mm self-propelled howitzer that had undergone initial tests of its firing capabilities and was scheduled to enter service in 2008.
Elgin, Okla., was slated to get a defense plant where the Crusader was to have been assembled, creating about 150 jobs for the town of 1,200.
Rumsfeld was disturbed that the Army's Office of Legislative Affairs had sought to fight the planned cancellation by preparing talking points for members of Congress to lobby for Crusader. When that became public, it appeared White was in danger of losing his job, but he stayed on.
White also became embroiled in a controversy over his former role as an executive with Enron Corp., the scandal-ridden energy trading company.
In testimony before a Senate panel last July, White said repeatedly he had played no part in manipulating California energy prices and knew nothing of other improprieties while he helped run an Enron subsidiary, Enron Energy Services.
At the hearing, White was questioned about trading strategies in California's electricity market detailed in December 2000 Enron memos. The memos described several schemes that critics say took advantage of California's power crisis, including one that involved Enron Energy Services.
White testified he was unaware of the strategies and memos until the Federal Energy Regulatory Commission made them public in 2002. He said the ploys would have hurt his subsidiary by driving up power costs that it could not pass on to its customers.
White worked for Enron from 1990 to 2001.
In an interview in March 2002, amid the Enron controversy, White said he would quit his Pentagon post should the federal investigation into Enron distract from his duties in the war on terrorism.
"I thought I could do something good for soldiers and their families," White said. "That is my focus. If I ever get to a point where that's no longer possible, it doesn't make any sense to stay when somebody else could do a better job."
White, a 1967 West Point graduate and Vietnam veteran, was trained as an armor officer. He rose to brigadier general during 23 years in the Army, retiring in 2000. 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.