WASHINGTON - The general picked by President Obama to take charge of the war in Afghanistan said yesterday that "significant growth" of the Afghan army and national police was the key to his strategy, but he acknowledged it would carry a high annual cost - four times the size of the entire Afghan economy.

Army Lt. Gen. Stanley McChrystal's testimony to the Senate Armed Services Committee, which is considering his nomination to lead U.S. and NATO troops in Afghanistan, suggested that the U.S. strategy in Afghanistan was likely to cost American taxpayers and NATO member nations billions of dollars for years.

The Afghan National Army is now 86,000 strong and the national police has 81,000 members. The United States has said it wants to expand the Army to 134,000 and the police to 82,000 by the end of 2011. McChrystal said he planned to boost even those figures.

However, maintaining and building the security forces to the current 2011 goals is estimated to cost roughly $4 billion a year, while Afghanistan's economy generates $800 million a year.

"We are building an army they will never be able to afford," a senior U.S. military official told McClatchy Newspapers. The official spoke on condition of anonymity because he wasn't authorized to talk to reporters.

Sen. Lindsey Graham, (R., S.C.) said the United States would have to foot the bill for years.

McChrystal, who now heads the U.S. Special Operations Command, also promised to reduce the civilian casualties in U.S. air attacks that are eroding Afghan support for the U.S.-led coalition.

"Our willingness to operate in ways that minimize casualties or damage - even when doing so makes our task more difficult - is essential to our credibility," he said.

Senators did not press McChrystal hard during the nearly three-hour hearing, and the Senate is expected to confirm him as early as tomorrow. Nevertheless, his nomination has generated some debate.

As special operations commander, he was responsible for the treatment of the detainees captured by U.S. special operations forces in Iraq and Afghanistan, and operations he oversaw in Afghanistan resulted in hundreds of civilian casualties.

He stressed he never endorsed abuse of detainees and "never will."

McChrystal also was special operations commander when former Arizona Cardinals safety Pat Tillman was killed in 2004. The Army initially said that the football player had been killed in an enemy attack, but later admitted that he had been killed by friendly fire.

McChrystal, who signed a letter recommending Tillman for a Silver Star despite questions about the circumstances of his death, said the mistakes in reporting how Tillman died were not intentional.

Sen. Jim Webb (D., Va.), a decorated Marine veteran of the Vietnam War, told McChrystal that the "Army failed the family." The general agreed and offered his apology.

McChrystal is to succeed Army Gen. David McKiernan, who had been less than a year in the post when Defense Secretary Robert M. Gates fired him last month.

McKiernan was ousted for several reasons, the senior U.S. military official said, including that Gates and Army Gen. David Petraeus, the head of the U.S. Central Command, believed he had moved too slowly in the effort to reach out to local security leaders in eastern Afghanistan to root out the growing Taliban insurgency.

McKiernan also was said to be opposed to adding a three-star general in Afghanistan to deal with day-to-day operations, something Pentagon officials considered necessary.