KABUL — Afghan President Hamid Karzai said today it will be at least 15 years before his government can bankroll a security force strong enough to protect the country from the threat of insurgency.

Speaking at a news conference with U.S. Defense Secretary Robert Gates, Karzai repeated his claim that Afghan security forces would take the lead in securing the nation within five years. But Gates suggested the U.S. can't wait that long.

"I would hope that we not only could meet the timelines that President Karzai has laid out, but that as more Afghans are trained we will be able to beat those timelines," Gates said.

Karzai's comments come a week after President Barack Obama said that while the U.S. was sending 30,000 more troops, they will start coming home in 18 months.

The top U.S. military commander in Afghanistan, Gen. Stanley McChrystal, has set the goal of building the Afghan security force to 400,000 by 2013, up from roughly 94,000 Afghan police officers and 97,000 soldiers.

When asked whether he would be able to sustain a larger Afghan force, Karzai said financial backing from the international community would be needed for years.

"For a number of years, maybe for another 15 to 20 years, Afghanistan will not be able to sustain a force of that nature and capability with its own resources," Karzai said.

Talking about U.S. troops, Gates said," On a gradual, conditions-based premise, we will be reducing our forces after July of 2011."

He added that the U.S. expects the draw down to be "a several-year process."

Meanwhile in Washington, D.C., congressional Democrats plan to give Gen. McChrystal a chance today to explain how he will use an infusion of 30,000 U.S. forces and whether he will be able to assure lawmakers that these troops will begin to be brought home in 18 months.

Many Democrats opposed to the escalation will try to get the general to say Obama's plan is inconsistent, congressional aides said. Based on his statements, it's clear McChrystal would have made different choices.