WASHINGTON - Afghan President Hamid Karzai raised doubts on Sunday that his country could take over responsibility for its security by July 2011, while U.S. leaders said the date was not a drop-dead deadline for Kabul.

U.S. President Barack Obama announced last week he would send another 30,000 troops to Afghanistan but would begin bringing them home in 18 months and start handing off responsibilities then to Afghan forces.

Karzai, speaking on CNN's Amanpour program, said Afghanistan would try to meet that timetable, but he suggested a two-year timeframe was more likely.

We will try our best, Karzai said. But the international community must have also the patience with us and the realization of the realities in Afghanistan. If it takes longer, then they must be with us.

Obama administration officials have been interpreting the president's goal since his announcement last Tuesday, trying to address political pressures at home while sending a signal of urgency to Karzai's government.

Obama has faced criticism from fellow Democrats for the troop increase and outrage from opposition Republicans about the deadline for a drawdown.

We're not talking about an exit strategy or a drop-dead deadline, Secretary of State Hillary Clinton told NBC's Meet the Press program. What we're talking about is an assessment that ... we can begin a transition, a transition to hand off responsibility to the Afghan forces.

Defense Secretary Robert Gates said Obama's speech was meant to show resolve while also communicating the urgent need for Afghanistan to recruit, train and move soldiers into the field. Gates, however, also played down the July 2011 date.

It's the beginning of a process, he told CBS's Face the Nation program.

In July 2011, our generals are confident that they will know whether our strategy is working. And the plan is to begin transferring areas of responsibility for security over to the Afghan security forces with ... us remaining in a tactical and then strategic overwatch position, he said.

AFGHAN TIMELINE, CORRUPTION

Karzai said he had no control over U.S. or NATO timelines but indicated Afghan forces needed two years to be ready to take over security responsibility for areas in the country.

We want to have in Afghanistan, in another two years, the ability to lead operations and provide security for the Afghan people in many parts of the country, he said.

By the end of five years term of -- of the current government, we plan to lead operations for the security of the Afghan people in all of Afghanistan, in the whole country. That is our objective.

Karzai's reputation was severely damaged after a U.N.-backed inquiry found nearly a third of votes cast for him in an August 20 election were fake. He pledged in his inauguration speech to name competent and honest ministers. His cabinet is expected to be announced in the coming days.

Obama has put significant pressure on Karzai to address the problem, and Afghan leader said he was doing so.

If and when at any time there is an occasion where we need to act on corruption with ministers, with officials, with anybody, we will do that, Karzai said, while adding that some in the international community had overplayed the issue.

I have fired people, and I will be firing people, he said.

Richard Holbrooke, the U.S. special envoy to Afghanistan and Pakistan, said corruption was a concern that had to be viewed in context.

We remain concerned about the corruption issue ... that is a matter of high concern for us, Holbrooke said on CNN's Fareed Zakaria GPS program.

At the same time, I think we have to be realistic, Holbrooke said, noting that Afghanistan was not an easily governable country and lacked a centralized government. It's complicated, its diverse, its very poor, he said.

(additional reporting by David Alexander and Paul Simao)

Afghanistan Hillary Clinton Barack obama