His comments came as Robert Gates, the US defence secretary, approved a request by Petraeus for an extra 2,200 US military policemen, in addition to 21,500 soldiers and 2,400 support troops being sent to Baghdad by the administration of George Bush, the US president.
The request for extra troops comes amid fierce opposition in the Democratic-controlled congress to the increase in troops and polls that show little public support in north America for expanding the size of the force.
"Peace in Iraq will happen when citizens realise that they can express their ideas and views more effectively... than with violence"
JBernar5, Toledo, USA
Send us your views
Democrats are pushing for a timetable for withdrawal of troops after widespread anger at the war handed them victory in last November's mid-term elections.
Gates last month assured congress that only about 2,000 to 3,000 support troops would be needed in addition to the combat forces that will add to the 141,000 US troops now in Iraq.
But Gordon England, the deputy defence secretary, told legislators on Tuesday that between 4,000 and 7,000 more support troops were required for the Baghdad security operation.
Gates said there were other requests that had been made for additional troops that had not yet been approved.
Asked about reports the additional 21,500 troops would have to stay in Iraq until early 2008, Petraeus said: "I've certainly not reached a conclusion yet about that.
"I think you generally think that if you're going to achieve the kind of effects that we probably need, I would think it would need to be sustained certainly some time well beyond the summer, but again we'll have to see."
Petraeus took command of US troops in Iraq last month at a critical time, having been appointed to oversee Bush's new strategy in Iraq, focusing on halting the daily carnage of suicide bombs and death squad killings in Baghdad.
At least 3,188 American soldiers have died since the US-led invasion of Iraq in 2003, according to Reuters news agency.
An estimated 655,000 Iraqis, 2.5 per cent of the population, have been killed as a result of the invasion, according to an estimate in October by the Lancet, the British medical journal, and the John Hopkins Bloomberg School of Public Health in the city of Baltimore in Maryland, US.
Some academics and politicians have disputed the estimate.