The unpaid leave, which will essentially cut the pay of civilian employees by 20 percent, is expected to save up to $5 billion, one of many cuts required as the Pentagon tries to slash $46 billion in spending by the end of the year.

The across-the-board cuts, known as sequestration, are due to take effect on March 1 unless Congress decides to delay them. They were mandated by the Budget Control Act of 2011 because lawmakers and the White House failed to reach a compromise on alternative spending reductions.

The Defense Department, which had warned for weeks about the furlough plan, has imposed a hiring freeze on civilian personnel and ordered the termination of many of its 46,000 temporary and contract workers. Officials said about 6,000 had already been laid off, with more likely to come.

The Pentagon has stressed that most civilian defense employees are not working at desks in Washington but are spread across the country doing jobs like teaching, nursing and maintaining equipment.

The greatest impacts will be in Virginia, which will be hit with lost payroll of $660.8 million; California, with $419.7 million; Maryland, with $359.3 million; Texas, with $290.8 million; and Georgia, with $203.1 million. Vermont will take the smallest hit, with lost payroll of $3 million.

Panetta announced the congressional notification in a message to department employees as he was traveling to Brussels for a NATO meeting, where he was expected to warn Western allies that looming budget cuts would affect U.S. contributions to NATO readiness.

REQUESTS FOR EXCEPTIONS TO BE REVIEWED

“We think the alliance’s readiness could be diminished if sequestration takes effect,” Pentagon spokesman George Little told reporters flying with Panetta to Brussels. He noted that bilateral training with European allies could be affected, as could rotational deployment of U.S. forces to Europe.

“You put this all together, lack of U.S. readiness equals NATO lack of readiness,” Little said, adding that Panetta had been “very unhappy” earlier in the day about having to issue the message on civilian furloughs.