Democrats are expected to gain Senate seats this election cycle, but a wider majority won’t necessarily mean a more liberal chamber.

Just as the conservative Blue Dog Coalition has forced House Speaker Nancy Pelosi (D-Calif.) to moderate her positions in the 110th Congress, a new band of centrist Senate Democrats could hold similar sway over Majority Leader Harry Reid (D-Nev.) next year.

In the Senate, a similar transformation is under way. About five new centrist Democrats stand a good chance of winning their election battles this fall. That, taken with four freshman centrists who joined the conference in 2007 and about a dozen others, could make for a center that could dominate legislative battles on healthcare, energy issues, immigration and foreign policy.

“I think [the election] will have a fairly significant impact because the [Senate Democratic] caucus will go from having a small group of centrists or moderates to being almost evenly divided between moderates and liberals,” said Matt Bennett, a vice president at Third Way, a centrist Democratic think tank.

Bennett said people who think a wider Democratic majority in Congress along with Barack Obama winning the presidency will translate into new policies that have long been sought by the party’s left wing are in for “a bit of a shock.”

The dynamics will likely be a bit different in both chambers. In the House, the Blue Dogs are known to be staunch budget-deficit hawks, and they stick together on some of their core conservative fiscal issues. In the Senate, the coalition is much looser, and their unity will likely depend on the issue.

The significance of the centrists in the Senate might lie in their ability to form coalitions needed to defeat filibusters. But reaching an agreement with the GOP may be limited because the Democratic electoral success is coming at the hands of Republican centrists who have historically cut bipartisan deals.

Most analysts expect Senate Democrats to hold between 55 and 57 seats next year, compared to the 51 they have now with two Independents who caucus with them.

Part of the shift is due to the recruiting efforts of Sen. Charles Schumer (D-N.Y.), who has spearheaded his conference’s election-year strategy the last two cycles. He was strongly criticized by the left after recruiting conservative Democrats, like Bob Casey Jr. in Pennsylvania, who oppose abortion. But Schumer silenced those critics after Casey and his other recruits won their election bids and gave Democrats a two-seat majority this year.

Schumer addressed the Democratic convention last month and appeared on onstage with former New Hampshire Gov. Jeanne Shaheen, a centrist who is challenging Sen. John Sununu (R-N.H.) this year. They were joined by a handful of liberal Democrats seeking Senate seats this year: Rep. Tom Udall of New Mexico, Jeff Merkley of Oregon and Rep. Tom Allen of Maine.

With those three, Rep. Mark Udall of Colorado, and the possibility of comedian Al Franken of Minnesota, the Democrats do have a chance of adding some more liberal voices to the caucuses.

But their centrists are likely to grow in number, too.

One of them is former Virginia Gov. Mark Warner, is a near certainty to win the open Senate seat in the Old Dominion State. He supports abortion rights and backs domestic partnership benefits for gays and lesbians. But he is opposed to earned citizenship for illegal immigrants, backs broader free trade and strongly supports the Second Amendment.

Governors-turned-senators, like Sens. Ben Nelson (D-Neb.) and Evan Bayh (D-Ind.), tend to legislate from the middle of the political spectrum, having had experience compromising with state legislatures. Should she defeat Sununu, Shaheen would follow that approach, analysts say.

Other future Senate Democrats could come from deep-red territory, forcing them to moderate their positions.

Anchorage Mayor Mark Begich has a strong chance this fall of unseating the longest-serving Republican senator in history, Ted Stevens of Alaska. Unlike the party left, Begich strongly supports opening his state’s Arctic National Wildlife Refuge to oil drilling and is an ardent Second Amendment backer.

Other conservative Democrats include anti-abortion rights candidate Ronnie Musgrove, who stands a good chance of winning in Mississippi, staunch Republican territory. State Sen. Kay Hagan has strong support from pro-abortion rights Democrats, but she hails from deeply red North Carolina and is a gun-rights supporter who says she will push to reinstate pay-as-you-go budgetary rules to offset new spending.

Making sure the Democratic Congress sticks to its pledge to offset new spending with either tax increases or spending decreases is a central tenet for Blue Dogs.

Rep. Mike Ross (D-Ark.), communications co-chairman of the Blue Dogs, said that keeping pay-go in effect would be the main goal for conservative Democrats next year.

“I think the new Democratic majority will move more toward the middle,” Ross said. “We are not defeating Republicans with liberal Democrats. We are defeating Republicans with conservative-to-moderate Blue Dog Democrats.”

If Democrats have a big night on Nov. 4, they stand a chance of winning Senate seats in two Republican strongholds: Kentucky and Nebraska, with Bruce Lunsford and Scott Kleeb, respectively.

“I think it’s an exciting time for centrist Democrats,” said Rep. Jim Cooper (D-Tenn.), a Blue Dog member.