WASHINGTON (AP) — U.S. military leaders and the American ambassador favor a residual force of 13,600 in Afghanistan after combat troops leave at the end of 2014, the chairman of the House Armed Services Committee said Wednesday as President Barack Obama faces political and military pressures on his upcoming decision on the size of the force.

A day after wrapping up his third trip to Afghanistan, Rep. Howard "Buck" McKeon, R-Calif., said a U.S. force of 13,600 combined with coalition troops of some 6,000 would be "the one that has the least risk going forward." McKeon said he met with Marine Gen. Joseph Dunford, the top commander in Afghanistan, during the trip and he favors a residual force of that size as does Ambassador James Cunningham.

"I think we dropped the ball on Iraq," McKeon said in an interview with a small group of reporters. "I don't want to see that happen in Afghanistan."

Obama is expected to announce in the coming weeks the size of the U.S. force after combat troops leave Dec. 31, 2014, with political pressure from a war-weary nation for the United States to end its involvement in Afghanistan. More than 2,000 Americans have died since 2001, more than 18,000 have been wounded and billions of dollars have been spent.

The 13,600 plus the additional 6,000 is far more than what U.S. and NATO leaders discussed last month at a NATO meeting in Brussels. Officials said then that they may keep a total force of between 8,000 and 12,000 troops in Afghanistan. Former Defense Secretary Leon Panetta acknowledged that was the range being considered, but insisted that no final decision had been made.

Since then, military officials have made it clear that they prefer a more robust residual force, pushing back against the lower number in advance of Obama's announcement. Last week, Gen. James Mattis, head of U.S. Central Command, said he personally recommended the U.S. leave 13,600 troops in Afghanistan and that he assumed the NATO allies would probably contribute "around 50 percent" of the U.S. total, which would be roughly 6,500.

"We have to send a message of commitment," Mattis told the Senate Armed Services Committee.

Republican lawmakers who have traveled to Afghanistan and met with U.S. military leaders have strongly expressed their support for that number. McKeon and Senate Minority Leader Mitch McConnell, R-Ky., have indicated their support for a significant presence.

Defense hawks in Congress such as McKeon are up against tea partyers and other fiscal conservatives determined to cut defense spending as the U.S. winds down the wars in Iraq and Afghanistan. McKeon said estimates show that the residual force would cost around $25 billion.

The chairman said it was critical that the United States work out a bilateral security agreement with Afghanistan quickly as well as settle on the size of the residual force. He said those concrete steps would help him in the May-June time period as the House works on a defense policy bill and he pushes back against the growing calls for immediately ending U.S. operations in Afghanistan.

During his trip, McKeon did not meet with Afghanistan President Hamid Karzai, who this past weekend accused the Americans of working in collusion with Taliban insurgents to keep Afghanistan weak. McKeon said Dunford has told Karzai to direct his frustration at him and added that the Marine has the right temperament to deal with the mercurial Afghan president.

McKeon did meet briefly with newly minted Defense Secretary Chuck Hagel during the trip, and he said the two were in agreement on the imperative of working out a bilateral security agreement.

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Donna Cassata can be followed on Twitter at http://www.twitter.com/DonnaCassataAP