The US presidential election moved into high gear Monday as two new opinion polls showed Republican John McCain taking the lead over Democratic rival Barack Obama.

McCain, a decorated war hero who based much of his early campaign on the strength of his experience, wrestled last week for Obama’s mantle of change with the help of his surprise vice presidential pick Sarah Palin.

A USA Today/Gallup survey showed McCain ahead of Obama 50 percent to 46 percent among registered voters, a turnaround from a previous poll taken by the newspaper just before last week's Republican National Convention.

That poll had McCain trailing Obama by seven percentage points.

A new Gallup daily tracking poll found McCain had moved into a 48 to 45 percent lead ahead of the November 4 election — his best performance since May.

Experts attributed the McCain rebound to his party’s convention and the surprise naming of Alaska governor Palin.

"He's in a far better position than his people imagined he would be in at this point." political scientist Larry Sabato of the University of Virginia was quoted by USA Today as saying.

McCain and Palin vowed to use their history of fighting'corruption to shake up Washington at a series of campaign stops after the Republican National Convention.

"In politics, there are some candidates who use change to promote their careers, and then there are those like John McCain, who use their careers to promote change," Palin told cheering crowds in Wisconsin.

"We’re going to win this election and let me offer a little advance warning to the old big spending, do-nothing me-first country second Washington crowd: change is coming. Change is coming.’ McCain said the next day in Colorado.

Obama ridiculed McCain’s promise of change and hammered the Arizona senator on the limping US economy, saying the Republican represented no change from Bush.

"John McCain, who is a good man and has a compelling biography. has embraced and adopted the George Bush economic platform." Obama said on ABC television.

The Illinois senator argued that voters would realize that the election was a choice between a new direction and discredited Republican policies.