Americans are increasingly pessimistic about the future but voters do not seem to be holding it against Democratic President Barack Obama, who slightly expanded his lead over Republican rival Mitt Romney this month, a new Reuters/Ipsos poll says.

Three months before the November 6 presidential election, nearly two-thirds of Americans think the country is moving in the wrong direction. Only 31 per cent say it is moving in the right direction - the lowest number since December 2011.

But Obama's lead over Romney among registered voters was 49 per cent to 42 per cent, up slightly from the 6-point advantage the president held a month earlier over the former Massachusetts governor.

The results of the monthly poll - in which a majority of voters agreed that the economy is the most important problem facing the United States - suggest that the Obama campaign's efforts to paint Romney as being out of touch with the concerns of middle-class Americans could be preventing the Republican from gaining momentum in the race.

"The overall 'right track, wrong track' is worse than last month - the news hasn't been great lately," said Ipsos pollster Chris Jackson. "But Obama seems to be, to some extent, inoculated against some of the worst of that."

The telephone poll of 1168 adults, including 1014 registered voters, was taken from August 2 to August 6.

During that period, the Labor Department reported that US employers hired the most workers in five months but that the nation's jobless rate had risen to 8.3 per cent from 8.2 per cent.

Even so, in a reversal from July, registered voters thought Obama was stronger than Romney in dealing with jobs and the economy, and with tax issues.

The poll indicated that 46 per cent of registered voters thought Obama was stronger on jobs and the economy, compared with 44 per cent for Romney. And on tax matters, 49 per cent saw Obama as stronger, compared with 38 per cent for Romney.

In an advertising blitz that has been focused on a dozen politically divided states, Obama and his Democratic allies have been hammering Romney's record as a private equity executive at Bain Capital, accusing him of plundering companies and shipping jobs overseas.

'KITCHEN SINK' STRATEGY

The Obama team's ads also have questioned why Romney - who has an estimated fortune of up to US$250 million - will not release more than two years of tax returns, and have suggested that Romney has paid far lower tax rates than most Americans.

"The Democrats' current strategy of just pummeling Romney on Bain and on the economy has been kind of a kitchen sink thing," Jackson said. "Even if it's not necessarily hurt Romney, it's given him no opportunity to build a lead."

Obama's new lead on the issue of jobs and the economy is particularly significant, Jackson said.

"That is the key issue in this race," he said. "For Romney to be able to make a convincing argument and to win the election, he's going to have to have a fairly significant lead over Obama on that measure."

Jackson said Romney - who has based his campaign on the notion that he would be better than Obama at dealing with the economy - likely needs to have at least a 5- to 8-point lead over Obama on the jobs and economy issue to win the election.

"There's certainly no case at the moment that Romney's building some sort of momentum toward victory here," Jackson said.

The Reuters/Ipsos survey, conducted over landline and cell phones, has a margin of error of 3 per cent for all adults and 3.4 per cent for registered voters.

- Reuters