Mitt Romney accused President Barack Obama on Wednesday of promoting "trickle-down government" policies that are burdening the US economy, as the Republican candidate sought to use a high-stakes debate to right his struggling campaign before the November 6 presidential election.

As polls showed Obama with a slight edge among voters, Romney was the aggressor from the start of a 90-minute encounter between the two rivals at the University of Denver.

Appearing poised as he stood side-by-side with Obama for the first time, Romney zeroed in on weak economic growth and 8.1 per cent unemployment that has left Obama vulnerable in his effort to win a second four-year term.

"Now, I'm concerned that we're on the path that's just been unsuccessful. The president has a view very similar to the one he had when he ran for office four years ago, that spending more, taxing more, regulating more, if you will, trickle-down government would work. That's not the right answer for America," Romney said.

The incumbent Democrat was quick to put Romney on the defensive about his proposals for overhauling the US tax system.

Obama said Romney was promoting the same kind of tax cut proposals that former President George W Bush pushed through Congress in 2001 and 2003.

"We ended up moving from surpluses to deficits and it all culminated with the worst recession since the Great Depression," said Obama.

ROMNEY NEEDS VICTORY MORE

Romney was in need of a victory at the debate to help him put his campaign back on a positive footing after a rocky few weeks.

The former Massachusetts governor was damaged by a hidden-camera videotape in which he said 47 per cent of voters were dependent on government and unlikely to support him.

Obama, holding a slight edge in national polls and leading Romney in some swing states where the election will be decided, was looking in the debate to do avoid harming his position as the apparent front-runner.

The debate moderated by PBS anchor Jim Lehrer was the best opportunity to date to reach large numbers of voters in an unfiltered way, with an estimated television audience of 60 million possible.

Both men have been under pressure to provide more specific details on how to get America's economy surging again after a prolonged recovery from recession.

Obama charged that Romney's plan to reduce income taxes by 20 per cent across the board and eliminate some tax deductions would leave middle-class Americans paying more taxes, an allegation that Romney vociferously denied.

"The fact is that if you are lowering the rates the way you described, Governor, then it is not possible to come up with enough deductions and loopholes that only affect high-income individuals to avoid either raising the deficit or burdening the middle class. It's - it's math. It's arithmetic," Obama said.

Replied Romney, "Virtually everything he said about my tax plan is inaccurate."

The debate was the first of three such face-offs scheduled in the next four weeks. Biden and Romney's running mate, US Representative Paul Ryan, will also debate once, on October 11. – Reuters