Two-thirds of the reductions that Mr. Obama will claim are from cuts in spending, including in many domestic programs that he supports. Among the reductions for just the next fiscal year, 2012, which starts Oct. 1, are more than $1 billion from airport grants and nearly $1 billion from grants to states for water treatment plants and similar projects. Public health and forestry programs would also be cut.

Home energy assistance to low-income families and community service block grants would be cut in half, and an initiative to restore the Great Lakes? environmental health would be reduced by one-quarter.

The administration readily concedes, even boasts, that the president will not win any race to outcut Republicans. In the House, Republicans are trying to slash up to $100 billion in the current fiscal year alone before they begin writing their own proposed budget for 2012 and beyond.

But the administration contends that its plan would leave the country in better overall fiscal health than the path Republicans envision. Even as they seek to downsize domestic programs, they would exempt the Pentagon from budget reductions, make permanent all the Bush-era tax cuts that are to expire at the end of 2012 and repeal cost-saving provisions of the health care law.

Mr. Obama would also extend the Bush tax cuts, but not for people whose taxable income is more than $250,000 a year. His budget does not count that proposed change as a savings; in fact, the huge revenue loss from extending the tax cuts for all income below that amount is included in his deficit projections for the remainder of the decade.

By 2015, the senior administration official said, Mr. Obama?s budget would show a deficit of just over 3 percent of the gross domestic product, down from three times that level, and at roughly the point that economists consider stable; it would hover around that point through 2021. But beyond 2021, an aging population and rising health care costs are forecast to drive annual deficits higher again.

With Republicans in charge of the House, Mr. Obama?s budget is more a statement of his priorities and philosophy than an actual template for federal spending and tax policy. Long-term budget projections ? and especially deficit forecasts ? are frequently unreliable because they are subject to so many political and economic variables. The point of Mr. Obama?s forecast is less to promise a specific result than to signal to voters and financial markets that he is serious about reducing annual deficits.

Mr. Obama?s budget will also serve as his frame for the debate with Republicans over the highly political act of writing next year?s budget ? even as he tests Republicans? willingness to compromise on the more divisive solutions to the nation?s long-range imbalances. ?This is the opening bid in a long process,? said Senator Richard J. Durbin, Democrat of Illinois and the second-ranking Senate leader.

Previewing his budget message, Mr. Obama has argued for weeks that cuts deeper than he is seeking could threaten the fragile economic recovery and that America?s future growth and competitiveness demand increases in programs for education, infrastructure, innovation and research.

Mr. Obama would reduce military spending and some health program costs, but neither party is tackling the unsustainable long-term growth of entitlement programs like Medicare or proposing to raise revenues significantly to close the budget gap.

?This is a budget that?s at that pivot point where we?re saying we now have to move from making sure the recovery takes hold, while being careful not to undermine it, to start to move in the direction of putting policies in place that deal with the deficit,? said the administration official, who spoke on the condition of anonymity in order to preview budget details, ?because if we don?t deal with the deficit, it becomes the potential next substantial economic challenge.?

The $1.1 trillion in total deficit reduction that the administration will claim through the 2021 fiscal year is measured from spending levels enacted by Congress and the president for the 2010 fiscal year. Comparisons of the impact of Mr. Obama?s new budget and House Republicans? proposals on deficits and the size of government are difficult to make until both budgets are available.

House Republicans will begin work on a 2012 budget after they finish trying to shrink current spending. But their proposed $100 billion cut for this fiscal year, already four months old, would translate over a decade into more than $1 trillion in deficit reductions, budget analysts say.