A shaven-headed general credited with being the driving force behind the United States troop 'surge' took over command of the American-dominated coalition in Iraq today, charged with finding a way to wind down US troop levels without sacrificing the security gains of the past 18 months.

Ray Odierno, a towering figure at 6ft 5in, took over from General David Petraeus in a handover ceremony at a Saddam-era palace near Baghdad. The ceremony was presided over by Robert Gates, the Defence Secretary, who said of the new commander: "He knows that we are at a pivotal moment - where progress remains fragile and caution should be the order of the day."

General Odierno, who is promoted to four star rank with his new appointment, was General Petraeus's former deputy and played a key role in persuading Congress to endorse the deployment of 30,000 extra troops early last year.

That marked a dramatic turnaround for a commander slated for being both too aggressive in his tactics and overly confident during his first stint in Iraq, when he was in charge of the 4th Infantry Division around Saddam Hussein's home town in Tikrit.

His troops won plaudits for their capture of Saddam in an underground bunker in December 2003 but were accused of fomenting the Sunni insurgency through their heavy-handed tactics against locals and Baathist elements.

General Odierno returned to Iraq in late 2006 to become General Petraeus's deputy after a stint at the Pentagon during which time he argued successfully for a change of strategy in Iraq. Mr Gates today paid tribute to the "incredible team" formed by the two men as the extra troops sent into Iraq early last year helped diffuse the insurgency.

Crucially, General Odierno, 54, had also become a convert to General Petraeus's 'hearts and minds' approach to the Iraqi mission, agreeing that counter-insurgency operations could only succeed if the population was on board.

On his first day in command today, the general underlined that philosophy with a "counter-insurgency guidance" document sent out to unit commanders and posted on the Multi-National Force website spelling out "How We Think", "How We Operate" and "Who We Are".

"The Iraqi people are the decision terrain," General Odierno writes in the document, which advises coalition forces to make an effort to understand the complexity of the conflict, promote reconciliation, embrace justice and have realistic expectations.

Under the "How We Operate" section, the general suggests that troops should, whenever possible, patrol on foot, rather than from the heights of an armoured vehicle. He writes: "Walk. Move mounted, work dismounted. Patrol on foot and engage the population - with the ISF [Iraqi security forces] in front whenever possible. Situational awareness can only be gained by interacting with the people face-to-face. Every patrol should have tasks designed to augment understand of the area and the enemy."

While violence is its lowest level of the past four years in Iraq, General Odierno will know as well as anyone that militants can still mount large-scale attacks. A female suicide bomber killed 22 people yesterday at a dinner celebration for police officers in Diyala province, only hours after two car bombs claimed a dozen lives in Baghdad.

In his address to the dignitaries and officers at today's handover ceremony, Mr Gates said that General Petraeus was leaving behind a very different Iraq to the one he faced when he took over in February 2007, when Iraq was on the brink of all-out civil war.

“Slowly, but inexorably, the tide began to turn. Our enemies took a fearsome beating they will not soon forget,” Mr Gates said. "Fortified by our own people and renewed commitment, the soldiers of Iraq found new courage and confidence. And the people of Iraq, resilient and emboldened, rose up to take back their country.”

In his reply, General Odierno agreed that Iraq was a different country to the one he first saw, but added: "We must realise that these gains are fragile and reversible."

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