Democrats will bring a $2.9 trillion fiscal 2008 budget blueprint to the House floor today and also may try to push it through the Senate this afternoon.

“I’m confident we have the votes to pass it, if everyone is here,” said Senate Budget Chairman Kent Conrad (D-N.D.), who noted he was asking the many Senator-cum-Democratic-presidential candidates to return from the campaign trail for the vote.

But Office of Management and Budget Director Rob Portman reiterated veto threats on spending bills that exceed President Bush’s request, setting the stage for a late-summer showdown with Congress on domestic spending.

“The new Democratic majorities are standing by their misguided plans for tax hikes and big spending increases,” Portman said. “Tax and spend is no way to balance the budget.”

The deal reached Wednesday by House and Senate Democrats would allow them flexibility to extend tax cuts for the middle class and significantly expand domestic discretionary spending. The agreement also projects reaching a $41 billion surplus in fiscal 2012.

The budget plan would allow a cap of $956 billion in discretionary spending in fiscal 2008 — $23 billion more than Bush requested, including $2 billion more in advance appropriations.

The budget provides for significant increases in veterans’ health care, education and other programs.

The budget assumes full funding of Bush’s request for military and war spending and about a 5 percent increase in domestic accounts.

To reach a deal, Democratic negotiators compromised on their “pay-as-you-go” principles to allow $180 billion in extensions of tax relief for the middle class and for estates. They included “triggers” that would allow the House to enact tax relief provided that a surplus is still projected for fiscal 2012.

The trigger mechanism essentially opens up a loophole allowing Democrats to pass popular extensions of middle-class tax cuts without finding offsetting pain — a political necessity given that the Senate voted 97-1 in favor of doing so.

However, the budget still assumes more than $700 billion in higher taxes because of the increasing impact of the alternative minimum tax and the expiration of other tax cuts, Republicans said.

Democrats said they assumed relief from the AMT this year, preventing 20 million additional taxpayers from being hit by the tax.

Democrats contended that the budget can be balanced without any tax rate increases but instead by improving tax compliance and shutting down offshore tax shelters.

Democrats also included a provision that would allow a major student loan overhaul to move later this year without the threat of a Senate filibuster, provided that it can muster at least $750 million in net savings over five years.

Conrad said that he agreed to include reconciliation language for student loan changes only after House leaders pledged to reduce the deficit by $750 million, or 10 times the original target proposed by the House.

“I do not favor reconciliation for this purpose, but increasing the amount they have to produce for deficit reduction by 10 times will … hopefully prevent others from going this route,” Conrad said.

Conrad dismissed the White House’s recent threat to veto any spending bills that do not hew to the president’s proposed discretionary spending cap.

“There’s a reason why the United States had no budget last year. There’s a reason 10 of the 12 appropriations bills weren’t considered last year. The reason is the White House had numbers that were unrealistic,” Conrad said. “The vast majority of the increase in spending in our bill … is for war and national defense.”

But over five years, spending actually would decrease as a percentage of gross domestic product, Conrad said.

Sen. Judd Gregg (R-N.H.), the ranking member on the Budget Committee, ripped the lack of cuts to entitlement programs.

“This budget contains billions in new spending on Washington programs — $205 billion over the president’s request over five years — and does absolutely nothing to address the $69 trillion long-term entitlement crisis we are facing,” Gregg said.

But House Budget Chairman John Spratt (D-S.C.) contended that the Democratic plan was more fiscally responsible than Bush’s, which would fail to balance the books under the Congressional Budget Office’s forecast.

“It posts smaller deficits than the president’s budget over five years; adheres to the pay-as-you-go principle and contains no new mandatory spending not paid for,” Spratt said.