The United States has a force of 157,000 in Iraq but there are plans to reduce this by at least 30,000.
At least 20,000 troops will be withdrawn by July 15, as the number of brigades is reduced from 19 to 15, according to military commanders.
The other 7,000 to 10,000 pesonnel are members of support units who will leave at the same time.
Referring to a possible halt to the planned withdrawl, Gates said: "I must say, in my own thinking, I am headed in that direction as well but one of the keys is how long is that period and what happens after that.
"It still has to be determined and decided by the president," he said.
Gates has previously said that he hopes to pullout about 100,000 troops by the end of the year.
Petraeus, who in April is due to make recommendations on US force levels for the second half of the year, last month suggested a pause to allow for security assesment.
It is not clear how long a pause Petraeus has in mind, but reports have varied from 30 to 90 days.
Gates arrived in Iraq on Sunday, shortly before the first anniversary of the so-called surge designed to improve security in Baghdad.
On Monday, two car bombs exploded almost simultaneously in Baghdad's southern neighbourhood of Jadriyah, killing at least 11 people and wounding 20.
A security official said the blasts occurred at Al-Huriyah, a busy square near an office which handles the affairs of tribal sheikhs from across Iraq.
Witnesses said a group of Awakening Council members were outside the office at the time and were among the wounded.
Another car bomb killed 25 people at a market in the village of Yathreb, near Balad, on Sunday.