GOP moderates in the U.S. Senate are seeking concessions from Democratic leadership in exchange for breaking with the Republican caucus and voting for cloture on Tuesday on major defense legislation containing “Don’t Ask, Don’t Tell” repeal, according to Capitol Hill sources.

One Republican source said among those seeking concessions from Senate Majority Leader Harry Reid (D-Nev.) are Sens. Susan Collins (R-Maine), Olympia Snowe (R-Maine, Scott Brown (R-Mass.), George Voinovoich (R-Ohio) and Richard Lugar (R-Ind.).

“There are several Republicans who are going to [Reid] saying, ‘Look, Mr. Majority Leader, work with us here because we have votes for cloture,'” the Republican source said.

It’s unclear what specific concessions the moderate Republicans are seeking, but they likely involve allowing GOP amendments to come to the floor on the fiscal year 2011 defense authorization bill, which contains language that would lead to “Don’t Ask, Don’t Tell” repeal.

“What was chaffing those members, as well as [Senate Minority Leader Mitch] McConnell (R-Ky.), was that … there was no consultation when Reid just said, ‘OK, boom! We’re going to have a cloture vote, and, oh, by the way, I’ve already put in my amendments and there’s no room for anything else,'” the Republican source said.

The three amendments that Reid has said he would allow on the floor are measures to strip the “Don’t Ask, Don’t Tell” repeal language from the bill; a measure to attach the DREAM Act, an immigration-related bill, to the legislation; and a measure addressing the “secret holds” senators can place on presidential nominees.

Another Republican source said Democratic leadership intends to attach the DREAM Act to the defense authorization bill as part of a manager’s amendment that also has language related to other defense items.

Reid’s office declined to comment on the concessions sought by GOP moderates or whether the majority leader would accept them.

The vote for cloture on the defense authorization is set for Tuesday at 2:15 p.m. A “yes” vote from 60 senators is required to move forward.

The Republican caucus has reportedly been telling GOP senators not to vote for cloture on the defense authorization bill because Sen. Reid is allowing limited amendments on the legislation.

The votes of Collins and Snowe are seen among repeal advocates as key to breaking a filibuster and moving forward with the defense authorization bill.

In conjunction with Servicemembers Legal Defense Network, pop singer Lady Gaga was set to appear at a rally in Portland, Maine, on Monday to urge the Maine senators to vote for cloture on the defense authorization bill.

SLDN Executive Director Aubrey Sarvis said in a statement promoting the event on Sunday that there aren’t yet sufficient votes to break a filibuster.

“We need Sens. Snowe and Collins on board; they’re key to us breaking the filibuster,” Sarvis said. “With the vote less than 48 hours away, we need everyone supporting repeal to call the Senate.”

(Sen. Susan Collins photo by Michael Key)