Later this month, under conditions of extreme security, Barack Obama will jet into Baghdad for policy discussions with America’s most popular general that could change the course of US involvement in Iraq.

The long-awaited meeting with General David Petraeus, commander of coalition forces in Iraq, is likely to prove the most dangerous encounter – politically and personally – of a week-long world tour that will carry the Democratic presidential candidate from high-profile meetings in London, Paris, Rome and Berlin to the military bases of Afghanistan and Iraq.

The candidate and the general have for months seemed at loggerheads over troop levels in Iraq, with Obama committed to a rapid withdrawal over the next 18 months and Petraeus arguing that a premature pull-out might endanger the success of the US military “surge” that has produced a sharp drop in violence this year.

Obama’s Republican rival, Senator John McCain, has repeatedly taunted the Democratic candidate for not having previously arranged a face-to-face meeting with Petraeus, whom many Americans credit with rescuing the US mission from disaster.

A clock on the Republican National Committee’s website noted that, as of yesterday, it was 916 days since Obama paid his only previous visit to Iraq.

“The trip has already turned into a trap,” warned Roger Simon, the chief political columnist of the widely read Politico website. “What is Obama going to learn from it?”

Last month McCain, who has visited Iraq at least eight times since the fall of Saddam Hussein, invited Obama to accompany him on a joint fact-finding mission to Baghdad.

The Illinois senator’s aides dismissed the offer as a “political stunt”, but the issue has become an embarrassment for Obama as the apparent success of the US surge has raised questions about his commitment to a steady withdrawal of one to two combat brigades each month.

“Is Obama the real deal or an eloquent phoney?” asked Morton Kondracke, a conservative columnist. “It would convince me that he was a daring politician if he saw General Petraeus and came back saying . . .‘This war was wrong at the start, but now we have to win it . . . we will withdraw – but only under conditions of success’.” With Republicans panting at the prospect of an Obama U-turn on a key plank of foreign policy, the Petraeus meeting promises a moment of genuine political theatre that is likely to be absent from the “grip’n’grin” photo opportunities lined up with Gordon Brown, President Nicolas Sarkozy, Pope Benedict and other leaders in Europe.

“I guess the question is, if indeed he’s going to Iraq and nothing that he sees will change or impact his decision-making on this, then why is he going?” asked Brian Rogers, a McCain campaign spokesman.

“If it’s just to make a political point, then it represents the kind of cynical politics that the American people are pretty sick and tired of.”

As the chief architect of the anti-terrorist surge, Petraeus is widely admired for reversing the tide of gloom that engulfed America when the original assault on Baghdad gave way to sectarian chaos.

Last year he was among candidates for Time magazine’s Man of the Year; last week he was confirmed by the US Senate as the next commander-in-chief of Central Command, a promotion that will put him in charge of US forces across a swathe of northern Africa, the Middle East and Central Asia.

Washington analysts are even speculating that Petraeus could become the next Dwight D Eisenhower – the second world war general who remained in Europe to lead Nato then returned to America to be elected president.

All this presents a formidable challenge to Obama, who will not want to be seen at odds with such a popular general.

The two have already crossed swords at a congressional hearing, although the senator subsequently defended Petraeus when a left-wing website labelled him “General Betray-Us”.

Despite Petraeus’s testimony to the Senate that “Iraq’s problems will require a long-term effort”, Obama has continued to emphasise in speeches and on his website that he wants all combat brigades out of Iraq by the end of next year.

That commitment persuaded many Democrats to back him against Hillary Clinton. But earlier this month Obama caused uproar among liberals by hinting that his policies might be “refined”.

Obama’s supporters argue it makes military and political sense to modify his stance in the light of experience on the ground.

The Republicans see his manoeuvring differently: they are portraying him as a cynical flip-flopper. “Why can’t Obama keep his story straight?” asked a recent e-mail from the McCain campaign.

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