His comments come as U.S. media reported that the United States is considering sending extra troops to Afghanistan next year.
Gates said the Pentagon would consult closely with NATO allies before making any decision to alter its military role in Afghanistan.
When asked by reporters to comment on discussion at the Pentagon about the possibility of taking over the command in southern Afghanistan, Gates said that this is "a matter that's going to be looked at over probably some period of time, primarily because it requires consultation with our allies."
During a visit on May 2 to the Red River Army Depot in Texarkana, Texas, the defense chief also said the United States needs to look at whether it continues to make sense to have two combatant commands involved in one country.
The United States has 34,000 troops in Afghanistan under two commands.
About 16,000 soldiers under U.S. European Command serve mostly in eastern Afghanistan as part of the 47,000-strong NATO-led International Security Assistance Force.
The other 18,000, which are involved in counterterrorism operations and training of Afghan security forces, are under U.S. Central Command.
Britain, Canada, the Netherlands, and Australia all have forces in southern Afghanistan, which has seen the worst of a rising tide of Taliban violence.
"The New York Times" reported on May 3 that the Pentagon is considering sending up to 7,000 more U.S. troops to Afghanistan next year to make up for a shortfall in contributions from NATO allies.
Citing unnamed senior administration officials, the newspaper said if the plan was to be approved, the number of U.S. troops in the country would entail at least a modest reduction in troops from Iraq.
It said U.S. forces would then account for two-thirds of foreign troops in Afghanistan.
The officials said the decision for more troops could be left to the next U.S. president, who will take office in January, and that few additional troops were expected in Afghanistan anytime soon.
The United States has recently increased its troop presence in Afghanistan. Some 3,500 Marines have been deployed to reinforce NATO forces in the south for seven months.
The United Sates and other NATO members have pushed their allies to provide combat troops and equipment to fill shortfalls in the south, but the response so far has been tepid.
According to "The New York Times" a dozen NATO countries, including France, have so far pledged a total of about 2,000 additional troops for Afghanistan, while alliance commanders have asked for 10,000.