Defense Secretary Robert Gates on Sunday sought to address a fundamental misunderstanding of President Obama's Afghanistan timeline.

In all likelihood, the Taliban will not be routed nor will President Hamid Karzai's government be corruption-free by the time the US begins drawing down troops in July 2011. The goal of the surge is not to solve Afghanistan's problems in 18 months.

Instead, the goal is to use the fist of a large force rapidly deployed to stagger the Taliban, breaking the Taliban's momentum and leaving an easier job for Afghan security forces going forward.

Speaking on two talk shows, Secretary Gates stressed that the off ramp that begins 18 months from now has no definitive end point. In other words, the US will begin to transfer some authority to the Afghans then, but how long that process takes will be the determination of generals in Afghanistan.

"I don't consider this an exit strategy," said Gates on ABC's "This Week." "It will be the same kind of gradual conditions-based transition province by province, district by district, that we saw in Iraq."

Reports suggest that Gates's support for Mr. Obama's plan was contingent on this point. Obama was insistent upon some explicit timeline in order to pressure Afghan officials to get their act together. But Gates demanded that the July 2011 date be merely a starting point, according to The New York Times.

On NBC's "Meet the Press," Gates said the timeline accomplishes both these aims, "giving the Afghans a sense of urgency" while leaving the back end of the commitment open.

Gates refused to be drawn in on questions of when all US forces might eventually be withdrawn from Afghanistan. But Secretary of State Hillary Clinton - appearing with him on "This Week" and "Meet the Press" - highlighted Mr. Karzai's own words as a guide to the potential arc of US involvement.

"He said that Afghan security forces would begin to take responsibility for important parts of the country within three years, and that they would be responsible for everything within five years," Secretary Clinton said on "This Week."

She agreed that the president's plan was not an "exit strategy."

Gates pointed out that the July 2011 date marks two years from the time troops deployed by Obama early in his term arrived on the ground in Helmand Province. The comment hints at the purpose for the surge.

Helmand is crucial to Afghan security because it the center of Afghanistan's massive opium industry, But British forces in Helmand had been all but overrun by the Taliban before US marines arrived this summer. The marines have been able to stabilize pockets of the province, but lacked the numbers to secure greater swaths of Helmand.

The surge aims to do just that, putting the Taliban on the defensive in its strongholds. But significant numbers of US troops will remain for the longer-term objectives of building Afghan police forces and cutting corruption in the Afghan government.

"We will have a significant number of forces in there for some considerable period of time after" July 2011, Gates told "Meet the Press."