Washington ? President Barack Obama, plunging into the rancorous struggle over America’s mountainous debt, will draw sharp differences with Republicans on Wednesday about how to conquer trillions of dollars in spending while somehow working out a compromise to raise some taxes and trim a cherished program like Medicare.

Obama’s speech will set a new long-term deficit-reduction goal and establish a dramatically different vision from a major Republican proposal that aims to cut more than $5 trillion over the next decade, officials said Monday.

Details of Obama’s plan are being closely held so far, but the deficit-cutting target probably will fall between the $1.1 trillion he proposed in his 2012 budget proposal and the $4 trillion that a fiscal commission he appointed recommended in December.

The speech is intended as a declaration of Obama’s commitment to seriously tame the deficit while outlining his long-term budget principles — key components of his campaign for re-election in 2012. After gingerly avoiding any discussion until now of cuts in the government’s massive benefit programs for the elderly and poor, Obama will acknowledge a need to reduce spending on Medicare and Medicaid while at the same time tackling defense spending and calling for increased taxes on the wealthy, White House officials said.

If that sounds like a reprise of last week’s budget fight that barely avoided a government shutdown, it isn’t. The stakes are far higher, the political risks greater and the goals more ambitious. At issue are long-term budget deficits and a $14.3 trillion national debt that many say could threaten the nation’s economy.

The cuts accomplished last week were for $38.5 billion over the next six months; the cuts envisioned now are for trillions of dollars over the next 10 years.

Obama’s speech, to be delivered at George Washington University, comes as Congress readies for a fierce fight over raising the nation’s debt limit. Republicans have vowed to use that vote as leverage to extract greater budget discipline from the Democrats and the president.

Setting the terms of the debate and the likely brinkmanship to follow, White House spokesman Jay Carney said on Monday: “What I’m saying is that we support a clean piece of legislation to raise the debt ceiling. … We cannot play chicken with the economy in this way.”

The president’s speech also comes amid liberal apprehension over recent Obama spending concessions and a desire among some Democrats to make proposed GOP cuts in Medicare a 2012 election issue.

House Republicans, led by the chairman of the House Budget Committee, Paul Ryan, last week unveiled a plan that would cut $5.8 trillion over 10 years with a major restructuring of the nation’s signature health care programs for the elderly and the poor. Meanwhile, six senators have formed a bipartisan group to work on their own plan to rein in long-term deficits by making changes to Medicare and Medicaid and examining a fundamental overhaul of the tax system that would yield additional revenue.

Obama is expected to concede a need for overhauling Medicare and Medicaid and to even make adjustments to Social Security, always considered politically risky territory. But he will distinguish his plan from the Republican budget, which would shrink Medicare by shifting the program to private insurers and send block grants to states to pay for Medicaid, the health care program for the poor.

Unlike the Republican plan, Obama is also expected to call for cuts in defense spending and for tax hikes, repeating his 2012 budget plan to increase Bush era tax rates for families making more than $250,000. Obama shelved that plan in a budget compromise with Republicans.

The Republican plan, on the other hand, would make the Bush-era tax cuts permanent.