The CBO's latest analysis shows the plan would pile up $6.39 trillion in cumulative deficits over a 10-year period, but that figure is about $294 billion less than the White House estimated in February for the same 2013-2022 period.

The long-term view provided a measure of positive news to Obama, who is seeking to counter Republicans' election-year attacks painting him as a tax-and-spend liberal who will rack up four straight years of trillion-dollar deficits in his first term.

It also gives Republicans new ammunition, including a nearly $1 trillion deficit next year and big debt and deficit targets that they aim to undershoot significantly when they unveil their own budget plan next week in the House of Representatives.

They are expected to seek cuts in discretionary spending and shrink outlays for the Social Security and Medicare programs for the elderly, while maintaining current low tax rates.

"It confirms that the President's budget accelerates our nation towards a debt crisis," said House Budget Committee Chairman Paul Ryan, who is leading the Republican effort.

"By contrast, the House Budget Committee will advance a budget next week that restores spending discipline, tackles the drivers of our debt, and makes good on the fundamental American promise: ensuring our children inherit a stronger America and greater opportunities than our parents gave us," Ryan said in a statement.

Neither the Ryan budget nor the Obama budget is expected to win congressional approval this year, but they will be fodder for the November election as both parties try to convince voters they have the better plan to tackle huge deficits and boost economic growth.

BUSH TAX CUTS KEY TO FORECASTS

The differences between the CBO and White House estimates of the Obama plan are due largely to the CBO's slightly more pessimistic near-term view of the economy and revenue growth, coupled with its projections of slower cost growth for Social Security benefits and lower interest costs later in the decade.

In fiscal 2013, the first full year in the president's budget, the CBO estimated the deficit would reach $977 billion, about $76 billion more than the White House estimated in February. The deficit then shrinks to $702 billion in fiscal 2014, about $34 billion higher than the White House estimate.

But the trend then reverses for several years, with the CBO offering lower deficit estimates through 2021.

There is only one year in which deficits fall below $500 billion - 2017 - but after 2015, deficits as a percentage of gross domestic product fall to below 3 percent, a level that many economists consider sustainable. The fiscal 2011 deficit of $1.3 trillion amounted to 8.7 percent of GDP.

The review confirmed that the Obama plan, which would raise taxes on the wealthy, boost near-term spending on infrastructure and keep in place some of the tax cuts enacted under former President George W. Bush, would pile up higher deficits over the next decade than would occur if all the Bush tax cuts were allowed to expire at the end of 2012.

But it also confirmed that the Obama plan would accumulate far less debt than if those cuts and other policies were left in place.

(Reporting By David Lawder; Editing by Peter Cooney)

• A Permanent Economic Emergency