Denver, Colorado/Washington - Democrats hope to position Barack Obama as the best candidate to restart a sluggish US economy, in an effort to convince skeptical working-class voters whose support could prove key in November's presidential election.

State governors from the battlegrounds of Ohio, Pennsylvania, Wisconsin and Iowa on Tuesday took to the convention stage in Denver, Colorado, on the second day of the opposition party's nominating convention.

All are states that have lost significant jobs in the manufacturing sector, and whose lower- and middle-class workers will be decisive swing voters in November.

"In Wisconsin and across the country today, people are working just as hard as ever, but they are finding their dreams further and further out of reach," Wisconsin Governor Jim Doyle said.

Obama, who is set to become the first ever African-American major- party nominee when he accepts the nomination Thursday, has struggled to appeal to rural and blue-collar voters who mostly supported his intra-party rival, Hillary Clinton.

It is a group that Republican White House hopeful John McCain hopes to peel off from the centre-left party, much like Ronald Reagan did in the 1980s, when a similar demographic become known as Reagan Democrats.

The sputtering US economy regularly polls as the top issue in the minds of US voters. Growth has slowed, petrol prices have soared, and plunging house prices have forced a record number of homeowners to default on their mortgages.

Democrats hammered McCain for "country club" economics that mirror the "outdated" policies of president George W Bush, whose approval ratings are at historic lows amid the current economic downturn.

Pennsylvania Governor Ed Rendell faulted Bush for energy and environmental policies that did little to wean the United States off its dependence on foreign oil.

"The only thing that (McCain) will recycle is the same, failed George Bush energy policy," Rendell said.

Republicans will have a chance to respond next week at their own convention in St Paul, Minnesota. McCain will formally accept the centre-right party's nomination on September 3.

Among the most hotly contested states ahead of November's general election will be Virginia in the traditionally conservative South, long a solidly Republican state but newly competitive amid changing demographics and allegiances.

Virginia has not voted for a Democratic presidential candidate since Lyndon Johnson in 1964. But an influx of younger, left-leaning voters into affluent northern suburbs outside the US capital of Washington has put the state back into play for the Democrats.

The prospect of capturing that elusive state is a big reason that Democrat Mark Warner, a popular former Virginia governor now favoured in his current US Senate bid, was chosen to give the keynote speech at the convention Tuesday night.

In a role that had catapulted Obama into the public eye at the Democratic convention four years ago, Warner took a page from Obama's speech book in calling for bipartisan unity.

"With the right leadership, there's no nation we can't out-hustle or outcompete," Warner said. "The race for the future will be won when old partisanship gives way to new ideas, and when hope replaces fear." (dpa)