ST. PAUL - Presidential rivals John McCain and Barack Obama, back on the campaign trail after their party conventions, clashed over the ailing U.S. economy on Friday as unemployment hit its highest monthly rate in nearly five years.

Hours after accepting the Republican nomination, McCain and running mate Sarah Palin opened a two-month sprint to the Nov. 4 presidential election in Wisconsin and Democrat Obama headed to Pennsylvania to tout their cures for the economy.

A new report showed the U.S. jobless rate unexpectedly shot up to 6.1 percent in August, adding to public worries about an economy that opinion polls show was already the top concern for American voters.

"Americans are hurting and we must act to create jobs," McCain said in a statement, promising to enact a jobs program and retrain workers for a changing market.

He rapped Obama's tax proposals, which include a large tax cut for lower- and middle-class workers but would increase taxes for the wealthiest Americans. "The American people cannot afford a Barack Obama presidency," he said.

Obama, an Illinois senator, said the job losses showed the need for change in the economic approach used over the last eight years under President George W. Bush. He said McCain would mean more of the same.

"Today's jobs report is a reminder of what's at stake in this election," he said in a statement. "John McCain showed last night that he is intent on continuing the economic policies that just this year have caused the American economy to lose 605,000 jobs."

The renewed battle on the economy came the day after McCain's acceptance speech concluded the Republican convention. Obama accepted the Democratic nod at his party's convention the week before.

Mindful of Bush's low public approval ratings, McCain has sought to distance himself from the current administration, and in his speech, he touted his credentials as a reformer and portrayed himself as the real agent of change in the race against Obama.

'I WORK FOR YOU'

"I don't work for a party. I don't work for a special interest. I don't work for myself. I work for you," McCain said in an address that included only passing criticisms of Obama after a four-day convention marked by scathing attacks on the Democrat.

"I've fought corruption and it didn't matter if the culprits were Democrats or Republicans," McCain said as Palin, the relatively unknown Alaska governor who he chose last week as his surprise running mate, watched from the stands.

McCain and Palin flew out of Minnesota immediately after the convention ended with the traditional sea of balloons, heading to Wisconsin for a morning campaign event and later in the day to Michigan and Colorado and on Saturday to New Mexico.

McCain trails Obama slightly in most national opinion polls as they head into the election but he promised the Republican faithful at the convention he would win.

Outside, police arrested 250 anti-war protesters marching to the venue after using flash grenades and teargas to herd them onto a bridge. Inside, McCain was interrupted several times by anti-war protesters. Police hauled two women out of the arena.

McCain has been one of the most outspoken supporters of U.S. military involvement in Iraq.

The Obama campaign said McCain talked about change but showed little interest in it.

"You can say 'change' 10 times in a speech, 15 times in speech. You can say 'reform.' The truth is, there's not an economic policy that was pointed to last night or at all in this convention that's one iota different from George Bush," Obama adviser Robert Gibbs said on MSNBC.

Opinion polls show majorities favor Obama's leadership on the economy, although McCain is usually favored on foreign policy issues.

With the conventions and the selections of running mates out of the way, the next big campaign milestone is the first of three debates, on Sept. 26 in Oxford, Mississippi.

Palin, the Alaska governor, meets Obama's No. 2, Delaware Sen. Joe Biden, in a debate between vice presidential candidates on Oct. 2 in St. Louis.

Palin has been shielded from most public events and has not done new interviews since she was picked for the job in a move that ignited a blaze of support among Republican social conservatives. She heads out on her own on the campaign trail next week.