President Obama's new budget plan was quickly dismissed Monday by Republican congressional leaders, but the document serves as a measure of his presidency - revealing vastly diminished ambitions and practical political calculations.

Two years ago, the popular new president had Democratic majorities in Congress as he released a far-reaching budget plan that introduced a New Deal sequel with dramatic proposals for health care, energy and the economy and a full embrace of government's central role.

The Obama of 2011, as demonstrated by Monday's budget rollout, seems resigned to operating in a far more constrained fashion as he plunges into policy combat for the first time with the GOP's House majority.

In declining to embrace the most politically sensitive ideas put forth by his bipartisan deficit commission - such as cutting Social Security benefits, eliminating the home mortgage tax deduction and making structural changes to the tax code - the president deferred tough decisions that many in both parties say are necessary to fix the country's fiscal problems.

The apparent tentativeness suggests that the man who once said he would rather be a good one-term president than a mediocre two-termer is, in fact, very interested in winning that second term.

"There is a hopeful interpretation of this strategy: The administration really wants to be involved in those conversations but doesn't believe that the ground has been adequately prepared for them," Brookings Institution scholar William Galston wrote on his blog Monday. Galston, who was a Clinton White House policy adviser, added: "There is a less hopeful interpretation - namely, that the administration doesn't want those talks to begin in earnest until after the 2012 presidential election."

Either way, Obama's budget can be viewed as a broad fiscal platform for his reelection campaign - and one that appears to match up nicely with public opinion. Polls have shown that Americans see federal spending and deficits as top-tier concerns, although their support falls off substantially once specific entitlement programs and aid for the poor are named as potential targets.

Polls also indicate that Obama needs to boost his budget-cutting credentials, with just 43 percent of Americans approving of his handling of the federal budget deficit in a January Washington Post-ABC News poll.

That may explain his planned cuts to summer-school Pell grants and heating-oil subsidies for the poor - proposals that allow Obama to portray himself as a hawk willing to stand up to liberals, even as Democratic senators stand ready to guard the programs from any substantive losses.

Meanwhile, Obama's pledge to trim the deficit by $1 trillion over the next decade, largely through tax increases on wealthier Americans and closing corporate loopholes, may be an effort to put Republicans in a box. The GOP says it wants to do even more to reduce the red ink, but that may require it to abandon its opposition to tax increaases or take the lead in identifying popular programs to trim or eliminate.

Republican leaders appear to welcome that opportunity, however, seeing it as a chance to portray Obama as a tax-and-spend liberal rather than a pragmatic centrist.

On Monday, Republicans accused Obama of using "gimmicks." Senate Minority Leader Mitch McConnell (Ky.) called the president's budget plan "unserious." Conservative groups such as Americans for Tax Reform accused Obama of raising taxes to make government bigger.

White House allies argued that, given the nature of politics today, the president would be foolish to expect a genuine policy debate over controversial and provocative proposals, such as those his deficit commission suggested.

"Floating proposals that swiftly get blown up as politicians jockey for political advantage does not advance the cause of fiscal responsibility," said Robert Greenstein, executive director of the left-leaning Center for Budget and Policy Priorities.

Greenstein said administration officials recognize that the budget proposal "does not go nearly far enough" to limit the debt in future decades. But he pointed to language in the document that invites discussions with the GOP on issues such as Social Security and transportation infrastructure.

McConnell has signaled a willingness to examine Social Security and other entitlements, and he and Obama have already forged one agreement - in December on tax cuts and unemployment benefits.

Still, despite Obama's efforts in recent days to court GOP lawmakers with private lunches and even a special home-brewed ale, Republicans clearly intend to intensify their opposition to the White House agenda. House leaders are planning extensive oversight hearings on the president's signature health-care overhaul and his use of federal regulations to impose restrictions on carbon emissions.

Now, with Obama's budget plan as a road map, the spending debate will draw even sharper contrasts between the governing philosophies of the president and the Republicans - a confrontation both sides appear eager to have.