By Jason Lange and Laura MacInnis
(Reuters) - The top contenders in the U.S. presidential race seem to have a simple plan for the gaping budget deficit: use it to strike fear into the hearts of voters.
Republican frontrunner Mitt Romney says President Barack Obama is such a big spender that he would trigger a Greece-style crisis if re-elected in November.
Democrat Obama says Republican candidates would balance the budget by slashing social programs older Americans rely on to pay their medical bills.
Polls suggest both approaches resonate with voters spooked by the biggest three-year surge in federal debt since World War Two, which has vaulted budget worries to the forefront of public consciousness and fueled the budget-slashing Tea Party movement.
"Debt is the main thing for me," said Brian Johnson, a mortgage banker in Manchester, New Hampshire, summing up his criteria for picking a candidate.
Johnson's comments were striking because for decades the country's national debt remained an abstract notion for most Americans - a scarily big number but one with little effect on people's pocketbooks.
But Americans are changing the way they think about the debt thanks to a noisy budget battle in Washington that prompted Standard & Poor's to downgrade the top-notch U.S. credit rating and raised the specter of what was once thought inconceivable - the United States defaulting on its obligations.
A headline-grabbing debt crisis that has forced tough austerity measures across Europe and led to social unrest in some countries has also made Americans sit up and take notice.
"It affects the economy and that affects myself and my income," Johnson said.
Millions of voters agree. Polls have consistently shown over the last year that the debt is near the top of their concerns, behind worries about the economy.
The data suggests debt will weigh heavily in November's presidential contest for the first time in years, not only because of the danger it poses to the economy, but because it crystallizes the ideological divide between Republicans and Democrats over the role of government.
Republicans including Romney believe market forces, not the government, should dictate the ebb and flow of the U.S. economy. Obama argues that government intervention in the economy is sometimes necessary and says his massive stimulus spending was crucial to keep the 2007-2009 recession from becoming a depression.
He also notes he inherited public coffers already sagging from costly wars and flagging tax revenues.
However, the fact remains that total federal debt has grown by about $4.6 trillion under Obama's watch.
To put that in perspective, Germany's entire economy generated less money last year. Put another way, Americans would have to cough up roughly $15,000 each to pay down all the debt taken on under Obama.
Still, it is hard for many people to get their heads around such giant piles of cash. This poses a challenge for campaigns trying to connect with voters on the issue.
"I'm paying bills. I can't even comprehend what a trillion dollars is," said John Kobzik of Windham, New Hampshire.
THE GREECE CARD
Romney is trying to connect with voters by giving vivid warnings about the risks of runaway debt. At rallies he has a prop - a giant electronic debt clock that shows the nation's total debt and the debt per taxpayer. The figures tick up while he is speaking.
The former Massachusetts governor, who is leading the Republican nominating race after easily winning the Florida primary on Tuesday, frequently suggests the United States could be the next Greece, a country that teeters on the edge of bankruptcy.
"We are headed to a Greece-type collapse," Romney said last week at the Republican candidates' debate in Tampa, Florida.
Such comments alarm voters who have seen images on their televisions of violent protests in Athens over budget cuts.
"You don't want to go the way that Europe is - and I am afraid that we will," said school bus driver Eddie Carr, who supports Romney.
Hammering Obama on the deficit could also help Republicans exploit another big worry for voters: the struggling economy.
Polls generally show that jobs and the economy are voters' top concerns this year. However, a survey by Pew Research in December asked the public what was keeping the economy down, and the answers were eye-opening.
About three-quarters of Americans saw the national debt as the biggest roadblock to prosperity. That outweighed worries about economic competition with China or government regulation.
Romney says he would tackle the deficit by repealing Obama's overhaul of the U.S. healthcare system, streamlining government and reducing the federal workforce.
Obama for his part has proposed a $4 trillion debt reduction plan that aides say he will seek to revive when he puts forward his 2013 budget proposal on February 13. Higher taxes on millionaires is a key element of that plan.
Polls showing widespread concern over the debt suggest the issue resonates beyond Republican voters or members of the Tea Party movement, whose budget-cutting zeal has been hugely influential in forcing Washington to make debt reduction a priority.
In the Pew poll, wide majorities of Democrats and independents also saw the debt as a major threat to the economy.
THE GRANNY CARD
With the public shaken by high unemployment, some voters worry aggressive measures to shrink deficits could leave people in the cold. Obama frequently paints the Republican vision of government as "you're-on-your-own" economics.
He says Republicans would "gut" funding for Medicare, the federal program that pays for elderly health care and which is often flagged as the top threat to long-term budget sustainability.
To punch his point home, Obama has brought up his own grandmother, who he says depended on Medicare as she lay on her deathbed in 2008.
Polls suggest this approach could have some bite. When Americans were asked in a Pew poll late last year to choose between fixing the deficit and keeping Medicare unchanged, they favored Medicare by a wide margin.
Still, it remains unclear if Obama's allusions to ailing grandmothers can neutralize Republican prophesies of doom and joblessness.
Only a quarter of Americans think the president has done a good job on deficits, a Gallup poll found in November.
"Obama is actually more vulnerable on the federal deficit than on jobs," said Frank Newport, editor-in-chief at Gallup.
The last time the debt played a significant role was probably the election of 1992, when third-party candidate Ross Perot helped raise concern about public spending.
Together with a weak economy, Perot's candidacy helped sink Republican President George H.W. Bush's bid for re-election and put his Democratic opponent, Bill Clinton, in the White House.
It is hard to predict if the debt will play such a large role in the election outcome this year. But the current trajectory of the national debt has probably not loomed over the economy so ominously in many decades.
Total federal debt last year was equivalent to about one year's worth of the country's economic output, up from about 70 percent just before Obama took office in January 2009.
That is a dramatic increase, although debt remains below the 1946 level of around 120 percent of GDP, and is well below the 160 percent level breached last year by Greece.
Many economists in the private sector expect Washington will avert a Greek-style crisis by eventually raising taxes and reining in spending on programs like Medicare.
"The prospect of an imminent U.S. crisis is pretty remote," said Michael Hanson, an economist at Bank of America.
But that does not mean Romney will pack away his debt clock any time soon as he seeks to exploit voter worries.
"This is something I care about for my children and grandchildren" said Randy Grant, a Vietnam War veteran in Columbia, South Carolina, who supports Romney.
"I don't want us to end up like Greece."
(Reporting by Jason Lange and Laura MacInnis in Washington; Additional reporting by Mary Milliken and Jason McLure in New Hampshire, Alistair Bell in South Carolina; Editing by Ross Colvin and Vicki Allen)