WASHINGTON - The Defense Department will furlough most of its 800,000 civilian employees for 11 days, a decision that Defense Secretary Chuck Hagel called "difficult" but necessary to meet mandatory federal spending cuts this year without harming national security.

"We tried everything we could not to get to this day this way," Hagel told an auditorium full of Pentagon civilians after he announced the decision. ". . . I could not responsibly go any deeper into cutting or jeopardizing our core missions."

Before $43 billion in mandatory defense cuts went into effect March 1, Pentagon officials warned that civilian employees could be required to take 22 days of unpaid leave. But a new spending bill approved by Congress at the end of March gave the Pentagon greater latitude to find budget savings, and officials were able to cut the forced furlough days in half.

Hagel said the unpaid days off would begin in July and last through September, when the fiscal year ends. The number of furlough days may be reduced further if additional ways of achieving savings can be found, officials said.

Tens of thousands of civilians who work at jobs deemed essential by the military services, including positions at military depots and Navy shipyards, are likely to be exempted from the furloughs, officials said.

Defense and military officials have been debating for weeks how to allocate the more than $7.5 billion that Congress allowed them to shift from lower-priority budget accounts into operations and maintenance programs.

Some officials favored using the money to reduce or eliminate furloughs, while top military officers said it should be used to reduce the impact on military operations, including flight and combat training and removing equipment from Afghanistan.

Hagel said that further reducing furlough days would further harm military readiness. The budget for military operations is facing a $30 billion shortfall due to the mandatory cuts, he said.

"I can't run this institution into a ditch," he said. "We've taken it as close to the line as possible."

Pentagon officials said they did not have an estimate for how much money the furloughs would save.