Washington - Leaving nothing to chance and taking no vote for granted, the two US presidential candidates kept up a frenetic pace Saturday as they plunged into the last weekend of campaigning before Tuesday's election.

Democratic Party presidential candidate Barack Obama is increasing his lead over Republican rival John McCain as the campaign enters its final phase, according to a poll published Saturday by the Washington Post.

It said 53 per cent of the electorate would vote for Obama, compared to 44 per cent for McCain. Obama also led in several key states seen as decisive in the election.

McCain campaign manager Rick Davis predicted a "comeback" in the final days, as both sides ramped up their advertising and volunteer operations and were backed up by several surrogate campaigners.

At a rally in Laramie, Wyoming, Vice President Dick Cheney endorsed McCain and his running mate Sarah Palin. "I believe the right leader for this moment in history is Senator John McCain," Cheney said.

"John is a man who understands the danger facing America, he's a man who has looked into the face of evil and not flinched, he's a man who is comfortable with responsibility, and has been since he joined the armed forces at the age of 17.

"He has earned our support and confidence, and the time is now to make him commander in chief."

In Pueblo, Colorado, Obama lashed out at the endorsement by Cheney, who he said "came out of his undisclosed location" to hit the campaign trail.

"I'd like to congratulate Senator McCain on this endorsement because he really earned it. That endorsement didn't come easy," Obama said. "Senator McCain had to vote
90 percent of the time with George Bush and Dick Cheney to get it. He served as Washington's biggest cheerleader for going to war in Iraq, and supports economic policies that are no different from the last eight years."

Cheney knows "that with John McCain you get a twofer: George Bush's economic policy and Dick Cheney's foreign policy ­ but that's a risk we cannot afford to take," Obama said.

The Democratic candidate swept through Colorado, Nevada and Missouri - states that voted for Bush in 2004. Meanwhile, his vice presidential candidate Joe Biden campaigned in Indiana, another Republican stronghold, where he accused the McCain campaign of going "way over the top."

"It is disappointing. I never thought I'd see this from a McCain campaign. They're calling Barack Obama every name in the book ... I don't recall it being more personally vicious."

McCain spent most of the day in Virginia, where a Democrat has not won the presidential vote since 1964, but where polls now show Obama leading.

The Republican candidate told cheering supporters: "You know how important it is for us to win here. You know how important it is that we put this country in the right direction. I need your help for the next three days."

Both campaigns claimed an edge in the early voting stakes in key battlegrounds including Florida, Nevada, New Mexico and North Carolina, as well as absentee ballots cast in other states.

David Plouffe, Obama's campaign manager, claimed more than 40 per cent of the total expected voters had already cast ballots in states that allow early voting. Higher turnout historically helps Democrats in presidential elections.

On Monday, McCain plans rallies in seven different states.

Obama's campaign was also taking its message into the Republican heartland - with advertisements in McCain's home state of Arizona, as well as North Dakota and Georgia. (dpa)