"That has to be a key factor in what I will recommend," he told ABC News in an interview at Camp Victory in Baghdad broadcast late on Tuesday.
Petraeus declined to be specific about the recommendations, which he gave to George Bush during the US president's surprise visit to Iraq on Monday.
But when asked if a reduction to avoid further strain on the military could happen in March, he replied: "Your calculations are about right."
Petraeus is due to present his assessment to congress next week along with the Ryan Crocker, US ambassador to congress.
ABC News quoted him as saying he is not feeling pressure from the political debate to present a "rosy picture" of the war.
He said: "This is not Ambassador Crocker and General Petraeus, who will decide what is to be done about Iraq.
"This will be a decision made at two ends of Pennsylvania Avenue."
While admitting it was still very dangerous in Iraq, Petraeus said the so-called "surge" in US troops had produced an "initiative, in general, against al-Qaeda, which is a change, and that is an important change".
"Eight of the past 11 weeks have seen the number of incidents, the number of attacks, come down, and to the point that they reached a level that's about the lowest in well over a year, I think," he said.
Meanwhile, 11 people were killed and 23 others wounded after a bomb exploded in a Shia neighbourhood of Baghdad on Wednesday, medical sources have said.
According to the police, the blast happened at around 8am in an area where minibuses stop to pick up people heading to work in the neighbourhood of Baladiyat, near the al-Hamza square in Sadr City.
The blast set at least five buses on fire.
A witness said there had been a number of explosions in Sadr City overnight.
Sadr City is a stronghold of Muqtada al-Sadr, a Shia cleric and commander of the Mahdi Army militia.
It has been a frequent target of Sunni fighters setting off bombs amid the country's Shia-Sunni sectarian conflict.
The US military also announced that four soldiers have been killed in separate attacks in Baghdad.
Three soldiers were killed and two wounded by a blast that hit their patrol on Tuesday, the military said.
Another soldier was killed and two more wounded during combat operations in a western Baghdad area.