US President Barack Obama and Republican Mitt Romney made their final urgent pleas to voters in a closing sprint through vital battleground states that will determine who wins race for the White House.

Both candidates sought to whip up strong turnout from supporters and to sway independent voters to their side in the last hours of a race that polls showed was deadlocked nationally.

Mr Obama had a slight lead in the eight or nine battleground states that will decide the race on election day tomorrow.

The latest Reuters/Ipsos national poll of likely voters, a daily tracking poll, gave Mr Obama a slight edge, with 48% support compared to Romney's 46%.

The difference was within the 3.4 percentage point credibility interval, which allows for statistical variation in Internet-based polls.

The president, with a final day itinerary that included stops in Wisconsin, Ohio and Iowa, urged voters to stick with him.

Mr Romney's final day included stops in Florida, Virginia, Ohio and New Hampshire.

The president, with a final day itinerary that included stops in Wisconsin, Ohio and Iowa, urged voters to stick with him.

The Democratic incumbent, appearing in Madison, Wisconsin, drew a large crowd that was warmed up by Bruce Springsteen and reprised the main theme of the campaign: who can do a better job on the economy.

"This should not be that complicated," Mr Obama said. "We tried our ideas; they worked. The economy grew. We created jobs. Deficits went down. We tried their ideas; they didn't work. The economy didn't grow, not as many jobs, and the deficit went up."

In Lynchburg, Virginia, Mr Romney told supporters: "One final push is going to get us there."

To supporters in Sanford, Florida, Mr Romney said: "If you believe we can do better, if you believe America should be on a better course, if you're tired of being tired, then I ask you to vote for real change."

The candidates are seeking to piece together the 270 Electoral College votes needed for victory in the state-by-state battle for the presidency.

Despite the close national opinion polls, Mr Obama has an easier path to victory: if he won the three states he was visiting on Monday - Wisconsin, Ohio and Iowa - then he would likely carry the day.

All eyes were on the Midwestern state of Ohio, whose 18 electoral votes could be decisive.

Mr Romney, looking for any edge possible, planned last-second visits tomorrow to both Ohio and Pennsylvania, aides said.

Visits to the areas around Cleveland and Pittsburgh would be aimed at driving turnout. And the Pittsburgh stop could be as much about Ohio as Pennsylvania, since many in eastern Ohio watch Pittsburgh television.

Mr Romney's path to the White House becomes much harder should he lose Ohio.

The state has been leaning toward Mr Obama - its unemployment rate is lower than the 7.9% national average and its heavy dependence on auto-related jobs meant the bailout to auto companies that Obama pursued in 2009 is popular.

Both campaigns expressed confidence that their candidate would win, and there were enough polls to bolster either view.

There were clear signs that Mr Obama held an edge. A CNN/ORC poll, for instance, showed him up in Ohio by 50% to 47%.

The close margins in state and national polls suggested the possibility of a cliffhanger that could be decided by which side has the best turnout operation and gets its voters to the polls.

Whoever wins will have a host of challenges to confront. The top priority will be the looming "fiscal cliff" of spending cuts and tax increases that would begin with the new year.

The balance of power in Congress also will be at stake, with Democrats now expected to narrowly hold their Senate majority and Republicans favoured to retain control of the House of Representatives.

In a race where the two candidates and their party allies raised a combined $2bn, the most in US history, both sides have pounded the heavily contested battleground states with an unprecedented barrage of ads.