General David Petraeus, the US commander in Iraq, will face questions on Capitol Hill tomorrow from all three presidential candidates knowing that the direction of the war, and his own future, hinges on who wins the presidential election in November.

In his progress report to two Senate Committees, General Petraeus will face Hillary Clinton and Barack Obama, both of whom are vocally opposed to his strategy of sustaining large US troop numbers in Iraq, and John McCain, a staunch supporter of his strategy who calls him one of the greatest generals in US history.

General Petraeus will argue that the “surge” of 30,000 extra troops has resulted in impressive security gains in Iraq, but only modest political ones. He is expected to recommend that troop levels be reduced to the pre-surge total by July, but will advocate a pause in any more reductions.

General Petraeus, who has more influence with President Bush over Iraq policy than any other military figure, knows that in less than a year he will have a new commander-in-chief, and that a Democratic general election victory will radically alter Iraq policy.

Both Mr Obama and Mrs Clinton have vowed to begin withdrawing US combat troops as soon as they take office. Mr Obama says he wants all combat troops out of Iraq by 2009. Mrs Clinton has promised to start withdrawing troops within 60 days of entering the White House. Mr McCain believes that to withdraw troops to below the pre-surge level would threaten any security gains achieved so far.

When General Petraeus last appeared on Capitol Hill in September, Mrs Clinton told him that his upbeat predictions about the surge required the “willing suspension of disbelief”. Now most Democrats concede that the strategy has significantly improved security. Yet the former First Lady, and Mr Obama, are expected to focus on the lack of significant political gains, the ongoing human and financial costs, and the recent fighting in the southern city of Basra. Polls show a clear majority of Americans believe the war was a mistake - but more hesitancy about a precipitous withdrawal.

General Petraeus will appear before the Senate Armed Services and Foreign Relations Committees alongside Ryan Crocker, the US ambassador to Iraq.

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