Speaker John A. Boehner (R-Ohio) is determined to adjourn the House for the year on Friday. The Senate plans on remaining in town until Dec. 20. It is a short schedule that forced leaders of the House and Senate armed-services committees Monday to scale back their ambitions and agree to move ahead with a modified version of the National Defense Authorization Act, one of the few “must pass” measures left for the divided Congress.

The defense bill is logjammed in the Senate, where lawmakers have failed to agree on a series of proposed amendments. With no hope of resolving disagreements over dozens of proposed changes to the original defense bill, negotiators agreed Monday that the House will vote on a modified version of the bill before leaving Friday and send it to the Senate, where it could be approved next week — ensuring that Congress passes the legislation for the 52nd consecutive year.

“This is not the best way to proceed,” Senate Armed Services Committee Chairman Carl Levin (D-Mich.) said in a floor speech. “But our troops and their families and our nation’s security deserve a defense bill, and this is the only practical way to do a defense bill this year.”

The decision to proceed with a modified defense bill means that a series of more-ambitious proposals by Sen. Kirsten Gillibrand (D-N.Y.) to rewrite military personnel rules will be considered as a stand-alone measure at some point next year.

The agreement on the defense measure came as Senate Majority Leader Harry M. Reid (D-Nev.) welcomed colleagues back for what he said he hopes will be “a short, two-week work period.” But he threatened — as he often does — to keep the chamber open over the next two weekends to complete a litany of tasks, including passage of a new budget and a farm bill. He also listed the possibility of debating a new round of sanctions against Iran, as well as plans to confirm new leaders at the Department of Homeland Security and the Federal Reserve.