Speaker John Boehner is playing defense ahead of Thursday’s House vote on a compromise fiscal 2011 spending bill after a new report showed the deal would have almost no impact on this year’s deficit, despite making $38 billion in spending cuts.

Late Wednesday, Republican bloggers at RedState, ConservativeHQ and National Review ripped into the deal made last week by the Ohio Republican, President Barack Obama and Senate Majority Leader Harry Reid (D-Nev.). Former Minnesota Gov. Tim Pawlenty (R), who is considering a presidential campaign in 2012, came out against it as well.

As first reported by Politico’s David Rogers, a new Congressional Budget Office analysis projects that the deal would trim this year’s deficit by a mere $352 million from last year’s spending levels by the Sept. 30 end of the fiscal year, if war costs aren’t included. If war costs are included, the deficit actually goes up $3.3 billion from the CBO’s earlier projections.

The study does confirm that the bill would cut spending authority by $38 billion, but it will take longer for those cuts to show up on the bottom line.

Boehner’s office released a fact sheet Wednesday night defending the deal, emphasizing that it includes real spending cuts, even if they wouldn’t all show up by Sept. 30.

“This bill will cut $315 billion in Washington spending over 10 years, $78 billion compared with the president’s request this year alone,” Boehner spokesman Michael Steel said.

The CBO’s surprising conclusions reflect the realities of budgeting in Washington — money often is appropriated one year and spent in another, and it’s hard to turn around spending on a dime.

Even the original House-passed bill, with its $61 billion in cuts, only trimmed outlays by $8.8 billion before Sept. 30, the CBO projected.

The small deficit number also reflects White House negotiators’ success in shifting cuts to slower-spending accounts, which the CBO determined were unlikely to have spent the targeted funds within the next six months. It also reflects the final deal’s inclusion of billions of dollars in increases for the military budget.

It’s not yet clear whether rank-and-file Republicans will jump ship over the new analysis.

Democratic aides, meanwhile, said that Boehner has yet to reach across the aisle for votes and that he better do so if he needs them.

“The usual ‘cross your fingers and hope it passes’ won’t work this time,” one senior House Democratic aide said.