WASHINGTON — Senators Obama and McCain may face increasing pressure to revise their ambitious economic proposals after the White House yesterday said the nation’s budget deficit is likely to be much larger than previously thought.

The Bush administration is now projecting a budget gap of $482 billion for 2009, a jump of more than $70 billion from its forecast in February. The number represents a record nominal dollar figure for the deficit, although it falls well short of the all-time high when measured as a percentage of the total economy.

The estimate came as part of a sobering economic report by the administration in which officials forecast a slower rate of economic growth — 1.6% — and higher unemployment than they had predicted earlier this year.

The larger deficit, they said, was a result both of the struggling economy and the bipartisan stimulus package that Congress approved and President Bush signed in January.

The White House budget director, James Nussle, acknowledged that the administration was “not happy” with the deficit, but he said it could be controlled with sound fiscal policy. “Near-term deficits are both temporary and manageable if, and only if, we keep spending in check, the tax burden low, and the economy growing,” Mr. Nussle told reporters. “Excessive spending beyond the president’s budget plan will make the problem worse.”

He warned against proposals from the Democratic-controlled Congress to increase spending and taxes, and he said the nation remained on track to achieve Mr. Bush’s goal of a balanced budget by 2012.

Democrats were dubious, however, and pointed out that the budget estimates include neither the housing rescue bill passed by Congress last week nor as much as $80 billion in funding for the wars in Iraq and Afghanistan.

Economists said the ballooning deficit would make it harder for either presidential candidate to make good on campaign promises for billions of dollars in tax cuts and new spending on health, energy, and other areas. “Both candidates are making commitments that aren’t funded,” a former Treasury official who is now senior vice president of the non-partisan Tax Foundation, Robert Carroll, said, adding that the new numbers would heighten pressure to raise taxes.

Messrs. Obama and McCain issued statements saying the deficit was a serious concern, but neither contender would specify exactly how the new projections would affect their economic platform.

“This should constrain what the candidates actually do once they’re in office,” the director of the Tax Policy Center at the Bookings Institution, Leonard Burman, said. “It’s probably not going to constrain what they say on the campaign trail.”

Mr. McCain, the presumptive Republican nominee, said in a statement that he is committed to his pledge to balance the budget by the end of his first term. “Today’s news makes that job harder,” he said, “but should not change our resolve to make the tough decisions and the genuine effort to reach across the aisle that are needed to ensure a lasting solution to the spending problem that threatens the very stability of our economy.”

He said his plan to keep taxes low would spur the economy and that Mr. Obama’s proposal to raise taxes on wealthy Americans and on capital gains and dividends would have the opposite effect. “It will not work to solve the budget mess,” Mr. McCain said. “His taxes would not raise enough over the next decade to cover his spending proposals, let alone make a dent in the budget deficit.”

For Mr. Obama, the dour deficit news arrived on a day when he was meeting with a group of high-profile economic advisers in Washington. They include a former Federal Reserve chairman, Paul Volcker, the investor Warren Buffett, and two former Treasury secretaries in the Clinton administration, Robert Rubin and Lawrence Summers. Mr. Rubin, who supported Senator Clinton in the Democratic primary, has drawn criticism in recent months for his role at Citigroup — where he is chairman of the executive committee — during a period in which the company wrote down more than $40 billion in losses and laid off thousands of employees. Mr. Rubin had served as a top economic adviser to President Clinton during his first term when the young administration decided to scale back several of its campaign proposals in favor of an aggressive deficit reduction plan.

The advisory group also included two former Bush administration officials who are neutral in the presidential race: Mr. Bush’s first Treasury secretary, Paul O’Neill, and a former chairman of the Securities and Exchange Commission, William Donaldson.

Mr. Obama made no mention of the new deficit projections during opening remarks at the meeting, which was then closed to the press. On a conference call afterward with reporters, a senior Obama adviser, Laura Tyson, was pressed repeatedly on how the increasing budget gap would effect Mr. Obama’s proposals. She said only that the Illinois senator had detailed how he would pay for each of his spending proposals and that he was committed to “long-run deficit reduction.” After declining to cite specific areas that might need to be revisited, she conceded that the deficit projections were not discussed at the two-hour meeting, which she said focused on ideas for a second stimulus package and other more immediate economic concerns.