House Speaker John Boehner (R-Ohio) and Senate Minority Leader Mitch McConnell (R-Ky.).(Karen Bleier/AFP/Getty Images)

The payroll tax cut extension package unveiled by House Republican leaders late last week is expected to come to the floor on Tuesday, a vote that will represent the latest test of Speaker John Boehner’s (R-Ohio) leadership.

In brief remarks to reporters last week after previewing the proposal to members of the House Republican conference, Boehner said that he felt “confident about our ability to move ahead” and that rank-and-file members had “received the discussion very well.”

Several members who had previously expressed reservations about extending the payroll tax holiday voiced support for the GOP plan as they emerged from last week’s conference meeting.

But if most Democrats oppose the measure, as House Minority Leader Nancy Pelosi (D-Calif.) and others have suggested, Boehner can only afford to lose the support of about two dozen of his 242-member conference when the bill comes to the floor.

The showdown will be the highest-stakes vote since late September, when a stopgap government funding measure unexpectedly fell short of passage amid near-unanimous opposition from Democrats as well as 48 GOP “no” votes.

Republicans on Monday lauded an announcement by Rep. Dan Boren (D-Okla.) that he will vote “yes” on the House GOP plan, which links the payroll tax cut extension to a host of other measures including a provision that would speed up a decision by the Obama administration on the Keystone XL oil sands pipeline.

“At a time when many are without work, it is time that we come together in a bipartisan way to pass this legislation which will create tens of thousands of new jobs,” said Boren, who plans to retire from the House in 2012. “I commend the Speaker for including the construction of the Keystone XL pipeline that is supported by business and labor.”

Boren added that he believes the measure “should attract votes from both political parties, because it takes initiatives supported by President Obama including the payroll tax cut extension and the extension of unemployment benefits, while also including initiatives supported by congressional Republicans like freezing federal worker pay.”

Senate Minority Leader Mitch McConnell (R-Ky.), who projected on Sunday that the proposal would get “significant” Democratic support, said on the Senate floor Monday afternoon that when -- not if -- the measure passes the House, later this week “senators will have an opportunity to do three big things with a single vote.”

“By voting for The Middle Class Tax Relief and Job Creation Act that we’ll soon get from the House, senators will be able to extend the temporary tax relief that working Americans continue to need nearly three years into this administration; prevent more job losses in the middle of a jobs crisis by blocking a new regulation on U.S. manufacturers; and facilitate the creation of tens of thousands of new jobs through the construction of the Keystone XL pipeline,” McConnell said. “One vote, three accomplishments.”

White House Press Secretary Jay Carney argued Monday that the GOP plan was “essentially suggesting that there is a political trade-off to be had, that extending tax cuts for middle class and working Americans should only occur in return for a political gift or an ideological item that some Republicans are insisting on.”

”I think we all need to step back and say, ‘What happened to Republican support for tax cuts?’” he added.

In his remarks opening the Senate on Monday, Senate Majority Leader Harry Reid (D-Nev.) reiterated his opposition to the House GOP plan and also took aim at Republicans for opposing Senate Democratic proposals that would have coupled an extension of the payroll tax holiday with a surtax on those earning more than $1 million a year.

“Millionaire job creators are like unicorns: They’re impossible to find and don’t exist,” Reid said, citing an NPR story in which a reporter encountered difficulty in tracking down millionaires who would be affected by the Democrats’ surtax.