Acknowledging they can no longer wait for their party’s nominee to emerge, Senate Democratic leaders have hatched an interim message strategy for their Conference that ties Republican presidential hopeful Sen. John McCain (Ariz.) with President Bush, trumpets 2008 as an election of change and stresses a broad economic platform focused on the middle class.

The leadership, led by Majority Leader Harry Reid (D-Nev.), will unveil the plan at a special Senator-only meeting this afternoon, where it will look to bring Senate Democrats into the fold and engage them in the strategy before the beginning of the Memorial Day recess. While specifics of the blueprint were being tightly guarded, Democratic Senators on Tuesday embraced the ideas behind it, agreeing they cannot wait for the conclusion of the protracted primary between Sens. Barack Obama (Ill.) and Hillary Rodham Clinton (N.Y.).

Rodell Mollineau, a Reid spokesman, offered little in terms of detail Wednesday, only to say: “Senate Democrats are going to continue talking about the issues that are most important to voters and highlight our efforts to bring about the change that Americans demand.”

Senate Democrats said that even if the presidential battle ends in early June as expected, it will take time for the presumptive nominee to organize his or her general election message — a critical two-month period they cannot afford to pass up. And, they insisted, Senate Democrats will not look to outline agenda items or a set road map that would trump or run counter to either candidates’ platform.

“We are trying to take proactive steps to define the differences between the two parties and differences in our agendas, while also being proactive in letting the American people know that we want to bring about change to the country,” one senior Democratic aide said on the condition of anonymity. “That goal is the same no matter who our nominee is.”

Another senior Democratic aide said Senators needed to talk about legislative solutions, and “it’s important we keep talking about what we would do with more Democrats in the House and Senate.”

Senate Democrats plan to push the interim message beginning in their districts over the recess and later on the Senate floor and through the media — honing in on a few key goals of trying to wed McCain to an unpopular Bush, talking up themselves as “change agents,” and laying out a plan to fix the struggling economy by making life more affordable for middle-income Americans. Democrats believe most of their party’s top priorities fall under that economic affordability umbrella, including gas prices, health care and education costs or job losses.

Although he hadn’t yet seen specifics, Sen. Bob Menendez (D-N.J.) agreed with the concept that Senate Democrats should play a more active role in developing and laying out a message for 2008, saying, “It serves the purpose of the nominee, but it is equally as powerful in our efforts to expand our majority.”

“In addition to the fact that obviously we want to be in concert with our nominee, there are races to be won across the country — and the economy is the No. 1 issue,” Menendez said.

Sen. Debbie Stabenow (D-Mich.) concurred that Democrats should fill the party’s message void until their presidential nominee is decided.

“It’s a good message for the American people to see that we are fighting for them and fighting for change,” Stabenow argued. “Our message fits very, very nicely with what our presidential candidate is going to be talking about.”

Senate Democrats have been working on a 2008 strategy for several months, but a tactical shift was necessary when it became clear that their presidential pick wouldn’t be known early this year, as predicted. House Democrats appear to be taking a separate, although not necessarily contradictory approach to their message planning, one that several sources said would undoubtedly involve a focus on the economy and McCain, but also be larger in scope.

Democrats indicated that part of the difference between the two chambers’ message comes down to the reality that House Democrats have the muscle to pass most of their agenda, while Senators cannot overcome what’s become an all but certain GOP filibuster of their initiatives. Reid has been pressing that point for months and urged Speaker Nancy Pelosi (D-Calif.) in a private leadership meeting earlier this week to help him ramp up that fight and help make his case for larger Senate majorities this fall.

Rep. Chris Van Hollen (Md.), chairman of the Democratic Congressional Campaign Committee, said Democratic leaders in both chambers agree that their summer message needs to “build on our record of legislative accomplishment,” such as already approved measures tightening lobbying laws, cutting interest rates on student loans and raising fuel-economy standards for cars.

He added that House Democratic leaders would continue talks with their Senate counterparts to refine their argument. “A big component of that is going to be the economy,” he said, while stressing national security issues will also be in the mix.

Speaking as if Obama will be the Democratic nominee, one of his most vocal backers, Rep. Artur Davis (D-Ala.), said: “The best way to support Obama is to advance a strong economic message. I have a hunch that as we head toward the fall campaign, we have an opportunity to have a huge edge over John McCain on economic issues and need to continue to drive that home.”

That sentiment has been festering among national Democrats for several weeks, particularly at the Democratic National Committee, where Chairman Howard Dean has been trying to summon Congressional leaders to help him mount a targeted offensive against the Arizona Senator. The DNC recently launched a national ad campaign targeting McCain, aiming to fill in the gap while Obama and Clinton continue their campaigns.

Challenging McCain is part of the Senate Democrats’ latest plans as well, with Reid looking to better galvanize lawmakers to more forcefully talk up how the GOP Senator’s policies represent a continuation of Bush’s tenure, and how he represents the “status quo” rather than Democrats’ model of change. Today’s Senator meeting will serve as both a refresher course as well as an orientation session in that effort, sources said.

The Senate Democrats’ effort came as Republicans on Wednesday attempted to attach a GI bill of rights measure backed by McCain to a Democratic labor union bill — a move that was widely seen as the beginning of the Senate GOP’s efforts to use the floor as a platform for supporting their presidential nominee.

As one senior Democrat put it, Senate Democrats are looking to do a better job branding themselves as the “change agents,” while simultaneously trying to “seal the bond” between McCain and Bush. Expect a shift in the Democrats rhetoric, the aide said, explaining that they will begin characterizing the opposing party as “Bush-McCain Republicans” rather than “Bush Republicans.”

“There’s widespread consensus that we are entering a transition period,” this staffer said. “The nominating process is winding down. We have about a month’s time before we have a nominee. It would behoove the Senate Democrats to soften the ground for a larger effort by Senators and the nominee to draw the lines of distinction.

“The idea would be to first storm the beach and clear the way for a broader conversation in the summer and into the fall,” the aide added. “If we do this right, the party could take cues from whatever the Senate hatches for the next few weeks.”

Tory Newmyer and John Stanton contributed to this report.