Washington - Republican John McCain never had much of a chance to defeat Democrat Barack Obama.

He campaigned under the mushroom cloud of an imploding economy, while shackled to the staggeringly unpopular presidency of fellow Republican George W Bush.

McCain, 72, couldn't compete against the fundraising prowess of an Obama campaign that outspent the Arizona senator by a 2 to 1 ratio, and a surge in turnout as US voters were fed up with Republican leadership under Bush and poised to embrace Obama's message of "change."

Yet the gritty war hero demonstrated the resolve that helped him survive more than five years as prisoner of war in North Vietnam, mounting a strong presidential run against insurmountable odds before graciously stepping aside and offering his support to Obama.

"I wish Godspeed to the man who was my former opponent and will be my next president," McCain told his disappointed supporters at a post-election rally in Phoenix, Arizona.

Obama handily beat McCain by at least 2 to 1 in the Electoral College, the state-by-state system that determines the winner in a presidential election but does not proportionally reflect popular sentiment.

But the popular vote was much closer. Obama held a margin of 52 to 47 per cent with the final vote count still pending.

Dealt a very bad hand, McCain's competitive performance was partly a reflection of his centrist, "maverick" history and the strength of his credentials on national security issues. But his 47-per-cent vote in a year that was a perfect storm against Republicans also shows that the 2008 elections may not represent a tectonic shift toward the left in US politics.

McCain could not hold onto several states that have been solidly Republican - including Virginia and Indiana - and failed to win in the biggest battleground states of Ohio, Pennsylvania and Florida, all getting hit hard by the current economic slowdown.

McCain's strengths on foreign policy, national security and the war in Iraq were swamped by the financial meltdown that gripped Wall Street last month and focused voters relentlessly on the economy, where opinion surveys showed voters with greater confidence in Obama.

"The American people have spoken, and they have spoken clearly," McCain said in his concession speech, standing alongside wife Cindy and his vice presidential running mate, Alaska Governor Sarah Palin.

McCain urged all Americans to support Obama as he tries to tackle the country's troubles, and he pressed supporters to set aside differences with Obama.

"These are difficult times for our country," McCain said. "And I pledge to (Obama) tonight to do all in my power to help him lead us through the many challenges we face."

McCain was unable to counter Obama's massive support from energized African-Americans in his successful bid to become the first black president. McCain never attempted - even subtly - to exploit the issue of race or tap into white fears or reservations about electing a non-white president.

Instead, McCain praised Obama's historic achievement and readily acknowledge the significance of the candidacy to African-Americans, who overcame generations of racial discrimination to achieve unfettered civil rights.

"America today is a world away from the cruel and frightful bigotry of that time," McCain said Tuesday night. "There is no better evidence of this than the election of an African-American to the presidency of the United States."

Despite the many handicaps that were not of his making, McCain made no excuses for the defeat.

"It is natural ... to feel some disappointment, but tomorrow we must move beyond it," he told supporters. "We fought as hard as we could, and though we fell short, the failure is mine - not yours." (dpa)