Gates, returning from a trip to Iraq, told reporters aboard his plane that perhaps one combat brigade would come out of Iraq ahead of schedule. He did not give a precise timetable.
Gates said that Gen. Ray Odierno, the top U.S. general in Iraq, told him that the security situation there is going better than expected.
President Obama has announced plans to withdraw American combat forces from Iraq by Aug. 31, 2010, leaving 30,000 to 50,000 U.S. troops in advising and training roles until the end of 2011.
U.S. officials had been worried that last month's scheduled handover of security to Iraqi security forces might erode security gains that had already been made. However, Gates said Odierno told him the security situation there was going well.
The defense secretary told reporters "there is at least some chance of a modest acceleration" in the pace of U.S. troop withdrawal.
Gatesat the future of the U.S. military mission in southern Iraq.
Gates flew from Amman, Jordan, to a command post in southern Iraq where U.S. troops are serving mainly as advisers to Iraqi forces. The advisory unit in Talil is a prototype for U.S. forces as they shift from front-line combat to support roles.
The secretary met with U.S. and Iraqi officers who have been patrolling together since July 15. He also saw the command center, a room where U.S. and Iraqi commanders meet each morning to go over coordination of patrols.