WASHINGTON, DC - SEPTEMBER 03: U.S. Sen. Carl Levin (D-MI) speaks to members of the media outside the West Wing of the White House after a meeting with President Barack Obama September 3, 2013 in Washington, DC. President Obama told reporters at the beginning of the meeting that he was confident he could get enough votes for his plan for military actions against the Bashar al-Assad regime in Syria. (Photo by Alex Wong/Getty Images)
U.S. Sen. Carl Levin (D-Mich.) (Photo by Alex Wong/Getty Images)

The U.S. Senate failed again Wednesday to move ahead with debate on the annual defense authorization bill, a key measure that sets military pay and policy.

Senators of both parties are hoping to complete work on the omnibus legislation by the end of the week, before beginning a two-week Thanksgiving recess. Failure to complete work on the bill this week leaves only a few days on the 2013 congressional calendar when the House and Senate will be in town simultaneously to broker a final deal.

"If we don't finish this bill this week, there cannot be a conference report, and then for the first time in 52 years there won't be a defense authorization bill," Sen. Carl Levin (D-Mich.), chairman of the Senate Armed Services Committee, said Wednesday afternoon.

The Senate on Wednesday had been debating two proposed amendments to the bill that would further revamp how the Pentagon handles thousands of estimated cases of assault and rape in the ranks each year. Sens. Kirsten Gillibrand (D-N.Y.) and Claire McCaskill (D-Mo.) spent most of the day leading an emotional discussion of the issue.

Majority Leader Harry M. Reid (D-Nev.) then came to the floor late in the afternoon and sought to move forward with votes on both proposals, but Republicans objected.

On Tuesday, senators voted down competing proposals over what to do with detainees held at the U.S. military detention facility at Guantanamo Bay, Cuba. The impasse once again complicates President Obama's goal of closing the detention facility, but also prevents language from being added to the defense bill that would make it harder to prosecute detainees in the United States or release them overseas.