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House Republicans voted today to reject a bipartisan Senate-passed bill for a two-month extension of a popular payroll tax cut, demanding a formal conference to work out their differences instead. But Democratic leaders in both the House and Senate have so far insisted on the Senate bill and publicly vowed not to appoint any conferees to the negotiations.

The standoff is jeopardizing the future of the tax cut, which benefits 160 million Americans and is set to expire at the end of the year.

President Obama quickly made an appearance in Washington to demand that House Republicans reconsider the Senate-passed bill.

"I need the Speaker and House Republicans to put politics aside, put aside issues where there are fundamental disagreement and come together on something we agree on," said Obama at the surprise appearance in the White House briefing room. "The American people are weary of this brinkmanship they're tired of it and they expect better."

But House Speaker John Boehner, asked moments later at a press conference, about the President's demand that Republicans "help out," said to raucous cheers from his colleagues, "I need the president to help out."

He argued that a conference between the House and Senate to work out their differences is the process the Constitution spells out for resolving differences.

By a mostly party-line vote of 229-193, House Republicans defied Congressional Democrats by passing a motion that the House disagree to the Senate Amendments to H.R. 3630, the Middle Class Tax Relief and Job Creation Act of 2011, and request a conference with the Senate. Seven Republicans joined an unanimous Democratic caucus in opposing the motion.

What does the payroll tax mean to your paycheck?

A senior GOP leadership aide said that with a narrow majority in the Senate, Democrats needed to first negotiate with Republicans to pass a Senate bill before Boehner would concede any ground from the House-passed bill.

"The Senate did produce a bill, and today Republicans will move to conference to reconcile the two measures," the aide said shortly before the vote. "That's how Congress works, and we see no reason to stray from regular order. This is the system our founders gave us, so let's take the next 10 days and make it work."

The Senate passed a two-month extension of the payroll tax on Saturday, and the House passed its own year-long extension last Tuesday.

Last night, Minority Leader Nancy Pelosi insisted she would not appoint Democratic members to the conference - a decision in line with Senate Majority Leader Harry Reid's declaration to sit out the negotiations.

"I don't think we should go to conference," Pelosi, D-Calif., said. "What we see now is a stalling action on the part of those who were never really for a payroll tax cut in the first place."

The seven Republicans voting against the motion were Reps. Charlie Bass, Jeff Flake, Christopher Gibson, Jaime Herrera Beutler, Tim Johnson, Walter Jones and Frank Wolf. Two House Republicans vying for the GOP presidential nomination, Reps. Michele Bachmann and Ron Paul, both missed the vote.

Once today's legislative business concludes, it's unclear what the next move might be in order to prevent the tax cut from expiring at the end of the year. Republicans are holding out hope that Pelosi and Reid will buckle under pressure and appoint conferees. Members say that later today the House is expected to recess, but lawmakers could be called back if and when there is a product to vote on from the conference negotiations.