Washington - Democrat Barack Obama and Republican John McCain clashed in their first debate Friday night over the war in Iraq and whether the next person to occupy the White House should meet with Iranian President Mahmoud Ahmadinejad.

The two candidates disagreed sharply over the future course in Iraq, with Obama pitching his plan to set a timeframe for withdrawing most US combat forces from Iraq. McCain charged that any premature pullout would allow Iraq to slide into chaos and endanger US interests in the region.

"You were wrong," Obama told McCain, who supported President George W Bush's decision to invade Iraq in March 2003 to topple Saddam Hussein's regime.

McCain sought to emphasize Obama's lack of experience by saying that some of the foreign policies his opponent advocates are "naive" and "dangerous."

"I'm afraid Senator Obama doesn't understand the difference between a tactic and a strategy," McCain said of the success that has been achieved in Iraq since Bush launched the buildup of US troops there in January 2007.

Obama and McCain held the first of three planned presidential debates at the University of Mississippi ahead of the November 4 election.

It marked the first time voters saw the men on stage together to discuss mostly foreign policy issues, but not until after the candidates outlined their positions on the financial crisis plaguing the US economy and sending shockwaves through global markets.

McCain, 72, was seen as having an advantage over the 47-year-old Obama on foreign policy, while polls show voters favouring Obama on the economy, which has become the top amid this month's Wall Street failures.

Both appeared confident in addressing both topics, and there was no clear-cut winner after the 90-minute exchange.

Obama said it was necessary to engage in dialogue with US foes to find areas of compromise and steadfastly defended his position of being open to meeting with Ahmadinejad, who has called for Israel to be wiped off he map.

"Without preconditions you sit down across the table from someone who has called Israel a stinking corpse," McCain said. "This isn't just naive, it's dangerous."

Both candidates blamed Bush for mismanaging the war following the ousting of Saddam's regime, but McCain touted the success of Bush's troop surge last year in bringing down violence in Iraq and said he had supported the move long before the president endorsed it.

"This strategy has succeeded, and we are winning in Iraq," McCain said.

"John, you like to pretend that the war started in 2007," Obama said, noting that more than 4,000 US soldiers have died in the conflict on which the United States has spent nearly 1 trillion dollars.

The debate started with a discussion of the financial crisis and Bush's 700-billion-dollar plan to rescue the troubled financial sector.

"We have to move swiftly, but we have to move wisely," Obama said.

Both candidates said that they backed Bush's plan - which would be the costliest government intervention into the free market in US history - but revealed little about their differences on the plan that is now being negotiated in Congress.

McCain called for consolidation of regulatory agencies that failed to prevent the current crisis on Wall Street and said that it was vital to "get spending under control in Washington," touting his record of opposing wasteful use of tax money and suggesting that a freeze in new spending for most federal programmes would be a good idea.

Obama called the current crisis a "final verdict" on the eight- year Bush administration and accused McCain of supporting the economic policies of Bush, who has the worst approval ratings of any president in more than 30 years.

The two men also differed over tax policy and the role of the federal government in the economy.

McCain said he would ensure that the US military has the necessary resources to finish off the Taliban and al-Qaeda in Afghanistan, while Obama sought to tie the failure to capture terrorist leader Osama bin Laden to Bush's decision, with the support of McCain, to invade Iraq.

McCain criticized Obama for not taking a tougher stance last month after Russia invaded Georgia in the dispute over the Georgian breakaway regions of South Ossetia and Abkhazia.

"He doesn't understand that Russia committed serious aggression against Georgia," McCain said.

Both candidates reaffirmed their support for allowing Georgia and another former Soviet state, Ukraine, to join the NATO alliance.

"Our entire Russian approach has to be evaluated because a resurgent and very aggressive Russia is a threat to the peace and stability of the region," Obama said. "Their actions in Georgia were unacceptable."