More than 650,000 civilian Defense Department workers will begin taking the first of their 11 unpaid days off next week, but the cut in salary they will see in the three months may pale compared to what officials worry could be larger scale layoffs next year.

Roughly 85 percent of the department’s nearly 900,000 civilians around the world will be furloughed, according to the latest statistics provided by the Pentagon. But while defense officials were able to shift money around to limit the furloughs this year, there are widespread worries that if automatic budget cuts go forward for 2014, thousands of civilian, military and contract jobs could be on the chopping block.

Defense Secretary Chuck Hagel is expected to provide senators with more details early next week on how the next wave of across-the-board budget cuts will affect the department, said Pentagon press secretary George Little. But while defense officials have not yet released details on the impact of the cuts, Gen. Ray Odierno, the Army’s chief of staff, has warned that as many as 100,000 more active-duty, National Guard and Reserve soldiers could lose their jobs if Congress allows billions of dollars in automatic budget cuts to continue next year.

Initial hopes that the number of furlough days could be reduced have largely been dashed. Instead, talk is focused more on how to slash spending in 2014. The department can only force workers to take 22 furlough days per year, thus the need for worker layoffs has been getting more traction to achieve savings.

In the coming weeks, however, civilian employees ranging from top-level policy advisers to school teachers and depot workers will not be answering their phones or responding to emails for one day a week through the end of the fiscal year on Sept. 30. The department estimates the savings will be between $1.9 billion and $2.1 billion.

Managers across the department have been given some flexibility in how they schedule the days off during each two-week pay period. But they also are dealing with complex legal requirements that in many cases prevent them from using military personnel to fill in for the absent civilians.

“There’s going to be perhaps some degradation of mission across the department, and because of reduced work schedules for 650,000 employees,” Little said. “We knew that going in, and we knew that would be a problem, and we’ve tried to take steps to ensure that top-priority missions across the department aren’t disproportionately affected.

In some cases, supervisors will try to accommodate workers who manage to find some other part-time, temporary job to help ease the fiscal pain, although they are limited in the types of employment they can take.

“We realize the impact that furloughs have on the morale of our civilian workforce, and it’s unfortunate that we have been forced into this series of choices,” Little said. “But there was really no set of good choices here.”

Civilians have been getting their furlough letters sporadically for the last few weeks. The letters tell them that during their furlough time, “you will not be permitted to serve as an unpaid volunteer, must remain away from your workplace, and are prohibited from performing any work-related duties.”

Civilians can appeal the furloughs once they have actually taken one of the unpaid days off.

The monetary impact for individuals varies widely, depending on salaries. But workers will effectively receive a 20 percent salary cut each pay period for the rest of the fiscal year. For a civilian making roughly $100,000 a year, that will mean about $1,600 in lost pay each month. Someone making $40,000 a year would get $600 less a month. Health care and other paycheck deductions would not decrease.