Gates, speaking at the end of a two-day visit to Afghanistan, gave no details about the possible troop increases.
U.S. President George W. Bush recently announced his plan to increase by more than 20,000 the number of American troops in Iraq.
Gates, who took over following the departure amid heavy criticism of Donald Rumsfeld, said it is important to consolidate military successes in Afghanistan. He said it is important to "keep the initiative" and not allow the Taliban to regroup.
Resurgent violence has fed public discontent in Afghanistan, where local and international officials have repeatedly cited insecurity as a major obstacle to maintaining order and rebuilding a country devastated by decades of war.
There are currently around 40,000 troops in Afghanistan, more than 30,000 of them with NATO's International Security Assistance Force (ISAF) and more than half of them American.
Gates acknowleged a security problem at the Afghanistan-Pakistan border, and said there are Al-Qaeda networks working on the Pakistan side of the border.
Gates said that while he has not yet given a thorough study of that situation, it is an issue that "we clearly will have to pursue with the Pakistani government."
Kabul and Islamabad have exchanged blunt words over perceived efforts to stem cross-border terrorism that undermines regional security.