The leading Senate Democrat on military matters pleaded with the upper chamber to start debating the 2011 defense policy bill, but he struck a pessimistic tone over the bill's chances to make it to the president's desk for the final signature.

The massive 2011 defense authorization bill is the vehicle for the repeal of the "Don't ask, don't tell" law — the ban on openly gay people from serving in the military.

"Even if we get 60 votes today to invoke cloture on the motion to proceed to this bill, and even if we're able to consider amendments and pass this bill in a few days, it will be a possibly insurmountable challenge to work out all of the differences with the House," Sen. Carl Levin (D-Mich.), the chairman of the Senate Armed Services Committee, said Thursday. "Over the last 10 years...it has taken an average of 75 days to conference the defense authorization bill with the House after we pass it. If we don't proceed on this bill this week, then invoking cloture sometime next week, even if we can do it, it would be a symbolic victory. And I don't believe that there would be enough time to hammer out a final bill before the end of this session."  

Democrats need at least two Republicans in order to have the 60 votes necessary to start debating the bill. Sen. Susan Collins (R-Maine), who supports repeal, has been negotiating with Democrats the process of debating the bill — that is amendments to the bill and enough time to debate them. It's unclear yet where Collins stands, but she did not agree on Wednesday to the Senate Majority Leader Harry Reid's (D-Nev.) offer to allow 15 amendments to the bill — 10 for Republicans and five for Democrats.

Reid might bring up the defense authorization bill to the floor on Thursday if the Senate fails to start debating other bills.

Reid had pushed to bring it up Wednesday but the problem was the pledge Republican senators took not to back any additional legislation until the Senate passes a bill funding the government for 2011 and a deal on tax cuts is complete. Reid postponed bringing up the bill at the GOP's request.