The exact number to be recalled remained uncertain.
Civilian Pentagon employees comprise about half the 800 000 federal employees currently furloughed.
Defence Secretary Chuck Hagel said a legal review of the "Pay Our Military Act," signed by President Barack Obama on Monday on the eve of the shutdown, would allow him to bring a still unspecified number of civilians back to work this week.
Salaries
The announcement came as Democrats and Republicans in the House of Representatives agreed to pay all furloughed employees retroactively once the government reopens.
It was a rare moment of co-operation in the House as the two parties were entrenched in their positions on the shutdown. The US Senate is expected to go along.
But the actions did not solve the basic problem - the failure of Democrats and Republicans to settle their political differences and agree on a bill to fund and reopen the government.
The House measure prompted Democratic Representative Louise Slaughter of New York to suggest that since the employees were going to get their salaries anyway, "why don't we just let them come back to work?"
Talk of using broader budget deals to bring the standoff to an end has picked up in recent days, but without any visible result.Funding level
Democrats say bills to fund the government and raise the debt ceiling could be resolved quickly if House of Representatives Speaker John Boehner permitted votes on simple, no-strings-attached measures.
But most House Republicans want strings attached, including one aimed at crippling Obama's signature healthcare law, popularly known as Obamacare, and Boehner has so far refused to promise votes on either, in part because he could face a revolt that might cost him his job.
Democrats have already begun efforts to force a vote on the shutdown using complex and time-consuming parliamentary procedures.
House Democratic leader Nancy Pelosi sent a letter to Boehner signed by 195 of 200 House Democrats, demanding a vote on a bill to reopen the government without any rollback in Obamacare.
Pelosi said if Boehner did so, they would agree to the Republicans' government funding level for the next six weeks, more stringent than the Democratic level, which has already been approved by the Senate.