After picking up at least five seats Tuesday, Senate Democratic leaders might claim a mandate to push an aggressive legislative agenda in the 111th Congress, but with a filibuster-proof 60-vote margin just out of reach, bipartisanship will still be at a premium.

Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) are expected to lead their parties again in a dramatically changed Congress, but it remains unclear whether the partisan dynamic that has paralyzed most legislation in the Senate over the past two years will change.

Still, an exuberant Reid predicted that he would have a much easier lift as he seeks to move the agenda of Democratic President-elect Barack Obama.

“I feel confident we’re going to be able to move things,” he said in an interview Tuesday night.

Although Reid and McConnell are collegial, they clashed repeatedly over procedural matters, particularly over the rights of Republicans to offer amendments — a situation that led the Senate GOP to block a record number of bills from coming to the floor in the 110th Congress.

McConnell still has enough troops to use the filibuster, but barely. Democrats will need to pick off only a minimal number of Republicans to break any GOP-led filibusters — a much lower threshold than the nine GOP votes that largely eluded Democrats during the past two years.

Reid said it would be “foolish” for Senate Republicans to continue attempts to block legislation in the chamber.

He noted that Sen. Susan Collins — who won re-election last night — and her fellow Maine GOP centrist Olympia Snowe could be decisive votes for Democrats.

“They’re not going to be able to filibuster now,” Reid said. “We have a few Senators from Maine, and we’re going to have [Arizona GOP Sen.] John McCain, who’s never been a filibusterer.”

Republicans also said McConnell would likely have to tread lightly with the handful of centrists in the GOP conference.

“Working with moderates is always a better option than trying to force them to do what you want,” said Senate GOP strategist Ron Bonjean, who previously worked for former Majority Leader Trent Lott (R-Miss.). “However, the Republican leadership knows it will need to pick its battles in winning them over. It should be expected that moderates will not always be with them.”

But overall, McConnell will be faced with a slightly more conservative conference, given the retirements of dealmakers such as Sens. John Warner (Va.) and Pete Domenici {N.M.).

Despite crushing losses and expected upheaval among House Republican leaders, Senate Republicans have repeatedly insisted that McConnell should not be blamed for the diminished minority and would likely be returned to the leader position during internal elections the week of Nov. 17. Other top Senate GOP leaders are likely to keep their spots as well.

Still, Republicans were already taking stock and talking about the need to return to their roots.

National Republican Senatorial Committee Chairman John Ensign (Nev.) argued that Senate Republicans need to “re-establish what the Republican Party is all about … [and] get back to this big tent Republican Party” that is united on fiscal conservatism. Although Ensign was not ready to call for a break from socially conservative ideologies, he said issues such as abortion or gay rights should not be at the core of the party.

“I think we lost our way on our fundamentals” in recent years, Ensign said, adding that “those are the issue that we can disagree on as a party.”

Sen. Jim DeMint (R-S.C.), while agreeing that a return to conservative fiscal principles was wise, took a decidedly more militant tone.

“We have got to clean up, reform and rebuild the Republican Party before we can ask Americans to trust us again. This must begin with either a change of command at the highest levels or our current leaders must embrace a bold new direction,” DeMint said in a statement.

Changes are unlikely to the Republican leadership slate — with the exception of NRSC chairmanship, which Ensign is vacating. But DeMint and other conservatives will represent a significantly stronger position in a substantially smaller Conference.

DeMint, Sen. Tom Coburn (R-Okla.) and other conservatives, who have often found themselves on the losing end of internal fights over fiscal policy, are expected to use Tuesday’s election results as a starting point for pushing for a more starkly conservative Republican brand.

Reid said he believes the new Senators joining Democrats will feel, as he does, that the country voted Tuesday night for moderate — not liberal — policies, despite Democrats dramatic gains.

“I think the country has moved to the center,” Reid said. “I think people want us to get things done.”

Earlier in the evening, Reid struck a bipartisan note when he told Democrats gathered at Washington’s Hyatt Regency that they should not see this election as a “mandate for a party or an ideology.” He said it was “to stop fighting over the things that divide us and start working on the things that [unite] us.”

Reid himself may feel it necessary to put the brakes on an overtly liberal agenda, given his own expected tough re-election in 2010 in a Western swing state. Asked Tuesday night about the pressure his own re-election would bring to his leadership, Reid said, “I’m just going to be who’ve I’ve always been.”

John Stanton contributed to this report.