Secretary Gates said that as much as he would like to see foreign troops leave Afghanistan, it is impossible to foresee when that might happen.
Gates spoke on Tuesday at a joint news conference at the Pentagon with French Defense Minister Herve Morin, who said on Monday that NATO should soon set a date for the start of such a withdrawal.
"I do not see that happening anytime in the near future. And I think it's impossible to put a date on when you might firmly say all the troops are coming out," Gates said.
President Obama recently approved a 45 percent increase in the U.S. troop presence in Afghanistan, to about 55,000. The American commander in Kabul said he will need the troops for the long term to fight the growing insurgency.
At Monday's news conference, French Defense Minister Herve Morin tried to clarify his earlier comments.
Morin said he never called for a withdrawal date, but rather said NATO should stay in Afghanistan as long as necessary, although not forever. He called for specific goals and milestones along the way in order to demonstrate to Europeans that there is a process in place that eventually will enable their troops to go home.
Secretary Gates has also called for goals in Afghanistan that can be achieved in three to five years. The Obama administration is currently reviewing U.S. policy toward Afghanistan and is expected to announce its plan before the NATO summit next month.
On Monday, Gates indicated that the talk of shorter-term goals in Afghanistan has caused concern among Afghan officials, including Defense Minister Abdul Rahim Wardak, who has been in Washington in recent days.
"I think that the conversations he had here in Washington last week provided considerable reassurance to him that nobody was talking about abandoning Afghanistan. But rather, we were trying to come up with shorter-term goals, where we could measure progress. And I think that he was considerably reassured by that," he said.
Gates also weighed in on the controversy about the date of Afghanistan's presidential election. The country's election commission set August 20 for the vote, so more U.S. troops will be available to help provide security.
But President Hamid Karzai has called for the election to be held next month. His term expires in May, and his opponents say he cannot stay in office after that.
Gates endorsed the August plan, but said there are concerns about President Karzai's status after May.
"I think it's a legitimate concern on the part of President Karzai. And I think the international community as well as the different elements in the Afghan government and parliament are trying to figure out the right way forward here," he said.
Gates said Afghan officials are trying to find a way to have a legitimate government between May and August.