President Obama's budget office on Tuesday lowered its projection for the federal deficit for fiscal 2015, estimating that the shortfall would be only $455 billion, rather than the $583 billion projected in February.

That deficit would be the smallest since before 2008, when the financial crisis caused tax revenue to collapse and emergency spending to rise.

"Under the president's leadership, the deficit has been cut by more than two-thirds as a share of the economy, representing the most rapid sustained deficit reduction since World War II, and it continues to fall," Office of Management and Budget Director Shaun Donovan said.

The $455 billion projected deficit would be $30 billion smaller than the fiscal 2014 deficit and the fifth consecutive drop in the annual shortfall.

The improvement in the budget outlook was driven by economic and technical reassessments. Tax revenue is on pace to be $72 billion higher than initially thought and spending $56 billion lower.

Donovan reiterated the president's budget proposal to cut deficits by an additional $1.75 trillion over the next 10 years, through health, tax and immigration reforms.

Under the president's budget, the deficit would shrink through fiscal 2016, then begin growing throughout the 10-year window. Federal debt held by the public would be mostly unchanged from 75.3 percent of national economic output today to 74.6 percent in 2025.

The Treasury Department reported Monday that June had a budget surplus of $52 billion, and that the deficit through the first nine months of the fiscal year, at $313 billion, was down 14 percent from the year before.