In his note to defense employees, Panetta said the department was “doing everything possible to limit the worst effects” of sequestration, “but I regret that our flexibility within the law is extremely limited.”

“The president has used his legal authority to exempt military personnel funding from sequestration, but we have no legal authority to exempt civilian personnel funding from reductions,” he added.

The Pentagon is required by law to advise Congress 45 days before furloughing any workers. The department is planning to put most civilian workers on unpaid leave for one day a week for 22 weeks between April and Sept. 30, the end of the fiscal year.

The military services also were formally notified of the decision on Wednesday and have until early March to ask the Pentagon for exceptions, officials said.

The Defense Department will review the requests and approve exceptions by mid-March, after which workers will receive 30 days notice of the impending furloughs, they said.

Hale told reporters that Pentagon officials felt compelled to move ahead with civilian furloughs because of increasing financial pressure on the department’s operations and maintenance account, which is used to pay for the war effort in Afghanistan.

“Furloughs are really the only way we have to quickly cut civilian personnel funding,” Hale told reporters at a briefing.