In a tactical role reversal from the years of absolute GOP control, House Democrats increasingly are turning to their Senate counterparts to take the first crack at much of the legislative heavy lifting of the 110th Congress.

From entitlement reform and immigration changes to Iraq policy, Senators are delving into new territory on Capitol Hill as the policy initiators, rather than simply serving as the burial ground for a slew of House-passed measures that failed the litmus test of compromise.

The Senate always has been the negotiating body, but these days, the deal making often is beginning in that chamber rather than ending there.

“It’s very different to move things with alacrity in the Senate, even with bipartisan support,” noted a GOP Senate leadership aide. “Democrats learned that early on. It took House Republicans a long time to learn that last year.”

With that in mind, Senators are working behind the scenes to craft deals on two of the most controversial topics before Congress: revisions to the Medicare and Social Security systems and immigration policy. Opinions vary widely on whether either issue actually will — or should — be addressed, especially during President Bush’s final two years in office, but at least in the Senate, discussions have been ongoing for weeks if not months.

Democratic and Republican lawmakers say Speaker Nancy Pelosi (D-Calif.) seems content to have the Senate take the lead on some of the more daunting issues this year. In part, those Members say, it is because the Senate, with a razor-thin 51-49 split, is the best determinant for whether legislation can garner bipartisan support and ultimately pass the entire Congress.

“The dynamic has changed,” explained a Senate Democratic leadership aide. “Democrats now control both bodies. Under the previous regime, the House Republican leadership could send bills over that in all likelihood would die under the Senate rules.

“The idea is if we can get the controversial bills through the Senate first, they’ve got a much better chance of moving through the House,” the aide said.

“Pelosi is looking to use the Senate as a filter, because if it can’t pass there it’s not going to pass,” the Republican Senate leadership aide added.

Senators in both parties say Pelosi hasn’t been shy about her desire to have the Senate move first on some of the more contentious issues, most notably on immigration reform. On that front, Senators have been holding talks for weeks — both bipartisan and partisan, with and without the White House — as they hope to craft a bill that can move before the electoral politics of 2008 take hold.

When asked last week about the House’s plan on immigration reform, Pelosi referenced the bipartisan immigration talks led by Sens. Edward Kennedy (D-Mass.) and John McCain (R-Ariz.), saying: “It’s a good place to start, it’s a place we hope to end up as well.”

“She wants the Senate to try to get” a bill crafted, said Senate Minority Whip Trent Lott (R-Miss.). “It’s going to be a challenge to come up with something that would be broadly accepted. But we’re working on it. We’re trying to get there.”

And while House Democratic leaders are hopeful the Senate can move ahead on such “heavy lift” legislation this Congress, lawmakers in both chambers question whether the strategy ultimately can be realized.

Numerous aides in both chambers pointed to the failed effort earlier this year to have the Senate take the first crack on passing an Iraq resolution condemning Bush’s proposed troop increase. When procedural hurdles and politics in the Senate made clear that Majority Leader Harry Reid (D-Nev.) did not have the votes to move forward, the House had to reverse course and act first.

The original plan was to have the Senate pass its resolution and have the House follow, with the idea being that any bill that could muster 60 votes in the Senate would pass with significant bipartisan support in the House. However, the House resolution attracted only 17 Republicans, and the Senate still has yet to pass a similar resolution opposing Bush’s policy.

With that serving as an early test, it remains unclear whether the Senate can have success initiating legislation on politically charged issues such as entitlement and immigration reform. Neither issue has advanced successfully in recent Congresses, and Democrats in power may be hesitant to negotiate with a lame-duck White House that previously has shown little desire to compromise.

Still, many lawmakers are putting on an optimistic front.

Sen. Lamar Alexander (R-Tenn.) said there’s a feeling that opportunities for legislative success are greater if the Senate takes the lead, saying there’s “no need for the House to send us” bills that won’t garner bipartisan support. Whether on immigration reform, health care policy or technology initiatives, the Senate may be in the best position to come up with legislation that could clear both chambers, and win Bush’s nod, he said.

“The Senate doesn’t work except by consensus,” he said. “It makes sense if we go first.”

And at least on immigration reform, that seems to be the widely accepted view. Rep. Howard Berman (Calif.), the second ranking Democrat on the House Judiciary Committee, said last week the plan from the beginning has been for the Senate to lead the way.

“Our assumption has always been that the Senate will go first for no other reason than they have approached the issue on a less polarized basis than the House,” Berman said, noting that the Senate was able to craft a bipartisan compromise in the 109th Congress, but the House passed a more partisan bill that never made it to conference with the Senate.

Sen. Byron Dorgan (D-N.D.) said that in part, the Senate is taking on some of the challenging subjects first, because at least on the Democratic side, many Senators believe they finally have an opportunity to make their mark on legislation. Under years of GOP control, Congress spent little time forging consensus across party lines, and now, Dorgan said that’s the only way legislation will become law.

“There’s a lot of pent-up desire to get things done,” he said. “Being in the minority, we’ve been frustrated for a good long while with the Republican agenda and we didn’t tackle the tough issues.”

The tactical decision to have the Senate move first on issues such as immigration, Social Security and entitlement reform is an indication that Democrats intend to run Congress differently than Republicans operated when they controlled both chambers. In particular, then-House Majority Leader Tom DeLay (R-Texas) and House conservatives believed it was imperative for the chamber to move first on any Social Security reform legislation to lay the marker for conference negotiations.

While Republicans in the 109th Congress never put together a Social Security bill, Members of the conservative Republican Study Committee had demanded that the House take the lead on the legislation.

This year, a handful of Senators, led by Sens. Kent Conrad (D-N.D.) and Judd Gregg (R-N.H.), have been in talks with the White House for weeks over whether and to what degree the system can be repaired.

And if House Ways and Means Chairman Charlie Rangel (D-N.Y.) has his way, that’s one area where the Senate will not be on deck first. Rangel, whose panel oversees the nation’s Social Security and entitlement programs, said he remains wary that Senators effectively can work through the procedural hurdles that dog the chamber and insisted he’s not privy to any “Senate-first strategy.”

“It’s difficult for the Senate to do anything,” he said. “I feel that taking hard votes, really, on the issues in my jurisdiction are about the ability to lead. … I wouldn’t hold back on trade, or fast track or Social Security, or tax simplification because the Senate’s tied up.”