Gates also said he disagrees with people who say it is time to get out of Afghanistan.
Several recent public opinion polls have shown Americans expressing declining support for the idea of sending more troops to the conflict and falling confidence in how the campaign is going. But at a Pentagon news conference, Gates challenged the public perception that the effort is getting away from the administration.
"I don't believe that the war is slipping through the administration's fingers," Gates said. "The nation has been at war for eight years. The fact that Americans would be tired of having their sons and daughters at risk and in battle is not surprising."
Gates argued that President Barack Obama's new strategy in Afghanistan has not been given a chance to work.
"I think what is important to remember is the president's decisions on this strategy were only made at the very end of March; our new commander appeared on the scene in June," Gates said, adding that the extra troops Obama ordered are not even all there yet, nor is the "civilian surge" he wants on hand to help.
"So we are only now beginning to be in a position to have the assets in place and the strategy or the military approach in place to begin to implement the strategy," he said.
The new U.S. and NATO commander, Gen. Stanley McChrystal, delivered a classified assessment Monday of how the war is going and is expected in the coming weeks to ask for more troops and money to turn the war around.
Obama is reading the report during his vacation at the Camp David presidential retreat north of Washington, his aides said.
Neither Gates nor the Joint Chiefs of Staff chairman, Adm. Mike Mullen, responded to a question about what the still-classified McChrystal report concludes. They repeatedly dropped references to some of the general's recommendations, with Mullen calling it a "frank and candid" look at how military forces can accomplish the Afghanistan mission.
Much of the debate around Afghanistan has centered on how many additional troops are needed there, and for how long. By the end of the year, an estimated 68,000 troops will be in Afghanistan, 21,000 of whom were ordered there by Obama early this year. Military commanders and State Department officials on the ground, however, say many more are needed to get the job done.
Mullen said questions of how many more troops might be sent was just a piece of the needs that the Pentagon soon will ask Congress to fulfill. "It's a piece - critical, but it's not total," Mullen said.