U.S. Defense Secretary Robert Gates said Sunday U.S. troops are expected to play a lead role in Afghanistan for another two to four years, as Afghan security forces gradually take over.

Appearing in NBC's "Meet the Press," Gates mentioned Afghan President Hamid Karzai's statement in his inaugural speech that Afghan security forces are to take over control in three years of important areas, and all of the country in five years.

"I think...we're in that neighborhood," Gates said.

But before Afghan forces are ready to take over, U.S. troops have to play a lead role in that country for "two to three to four years."

After months of review, the Obama administration on Tuesday renewed its strategy for Afghanistan by sending 30,000 fresh troops. The U.S. forces stationed in Afghanistan would reach about 100,000 after the surge. He also announced troops would begin to come home starting July 2011.

If conditions permit

"We're not talking about an abrupt withdrawal. We're talking about something that will take place over a period of time," he said, noting the bulk of nearly 100,000 forces in that country by 2010 summer won't leave in July of 2011, only "some, handful, or some small number, or whatever the conditions permit, will begin to withdraw at that time."

By combining a troop increase and a withdrawal timeframe, Obama intends to balance "a demonstration of resolve with communicating a sense of urgency to the Afghan government," Gates said. He said this way Afghan government would have to step up military recruitment, training and deployment.

In order to sell the new Afghan strategy to a skeptic U.S. public, Gates, along with Secretary of State Hillary Rodham Clinton, appeared in three major TV talkshows Sunday, talking about the surge and the exit strategy. Opinion polls have suggested it's tough work. A recent Pew Research Center poll found just 32 percent of respondents favored sending more troops into Afghanistan, while 40 percent wanted fewer.

The withdrawal timeframe also stirred mixed reactions, with Republicans worried U.S. enemies would be emboldened by it.

Gates rejected such suggestions. He told CBS's "Face the Nation" that Taliban members read newspapers and are able to determine public opinion in the United States and Europe.