The partisan discord that nearly paralyzed the Senate for the past few years may finally have been softened by rule changes intended to end stalling tactics and force the two parties to work together on legislation. The infamous efforts by the minority party to block legislation, including "secret holds" by senators and demands that bills be read on the Senate floor, were ended. And Republicans, who now control 47 votes to the Democrats' 53 votes, have agreed not to filibuster when bills are brought up for debate, a move that in the past prevented many measures from ever being considered on the Senate floor.

But Republicans didn't just give away the filibuster, the most powerful parliamentary tool the minority party has to ensure it's heard, for nothing. Majority Leader Harry Reid, D-Nev., promised the GOP that, in exchange for not stalling bills, they would be allowed to amend legislation, an opportunity Republicans say they've been denied.

Restrictions on the use of the filibuster, however, represent only an informal agreement, so if Reid denies GOP amendments on a bill, Senate Minority Leader Mitch McConnell, R-Ky., can revive the filibuster to block that bill from debate. It takes 60 votes to break a filibuster.

"We are making these changes in the name of compromise, and this agreement itself was constructed with the same respect for mutual concession," Reid said.

The new rules come at a time when Republicans and Democrats are calling for more cooperation and civility for the sake of getting things done. The rules' first test will come as soon as next week when the Senate considers a bill reauthorizing the Federal Aviation Administration. That bill, which the airline industry says would boost safety and efficiency, has been on hold since 2007 because of partisan disputes.

In light of the new ground rules, Reid promised a lengthy debate on the FAA bill and an opportunity for the GOP to amend it, which some believe will help ensure the bill's passage.

Robert Dove, a former Senate parliamentarian, said the rule changes could revive the kind of cooperation Capitol Hill has not seen in many years.

"What will happen now is there will probably be a lot more Republican input into what is in those bills, which will make the process smoother," said Dove, parliamentarian in the 1980s and again from 1995 to 2001. "You will have to have bipartisan support to pass things."

Some political observers, however, say differences between the two parties limit any chance for real compromise.

Sarah Binder, an expert on congressional and legislative politics at the Brookings Institution, noted that leaving the filibuster in place could still allow Republicans to block any final votes on bills.

"And what if one of the Republican amendments is to repeal the health care law?" Binder said. "Then what is Reid going to do? I don't really see how this will smooth the waters all that much."

The rule changes fall far short of the elimination of the filibuster originally sought by a group of junior senators. Instead, party leaders struck a deal that would leave the filibuster in place in this Congress and the next. Democrats were hesitant to abolish the filibuster that now gives Republicans an edge because, after 2012, Democrats may be in the minority.