The moves come nearly seven years into the war in Afghanistan, a conflict that has claimed more than 500 American lives. The last two months have been among the deadliest in Afghanistan for American forces, who are trying to contend with a sharp increase in attacks by Taliban militants, some of them staged with support from insurgents based in the remote tribal areas of neighboring Pakistan.  Pentagon officials say they hope the creation of a more unified command structure under General McKiernan will help to coordinate all forces in Afghanistan — most notably American units near the Pakistani border in eastern Afghanistan, which have operated independently of the NATO-led force in charge in southern Afghanistan.  “General McKiernan is in the best possible position to most efficiently and effectively deploy all of the resources to the benefit of the overall mission,” said Geoff Morrell, the Pentagon press secretary. “This creates one commander in country and in charge of all forces, and establishes a structure to deploy them as best suits the mission and to improve synchronization among all military assets.”  In the months ahead, NATO and the United States will nevertheless continue to pursue somewhat different missions in Afghanistan, Pentagon officials said, and the new command structure will not result in a merger of the two missions.  NATO took command of the nationwide mission to stabilize Afghanistan in 2006. The allies expected to face little direct combat and to focus on reconstruction and on maintaining security in areas that were relatively calm.  In contrast, the American-led mission in Afghanistan has focused from the start of the war on combat operations to capture or kill insurgents and terrorists, as well as on training Afghan security forces, counter-insurgency and reconstruction.  Although the situation has significantly changed, some allied units operate under strict constraints placed by their home governments that prevent them from participating in certain kinds of combat missions, which American officials have said is a major obstacle to beating back the Taliban.  Pentagon policy makers said one goal of the command restructuring would be to allow the movement of American and allied troops — including the British, Canadian and Dutch soldiers who participate in a full range of combat missions — to support one another in a more seamless fashion. It remains unclear if the change will persuade the militaries operating under restrictions to take on additional battlefield responsibilities.  Because of the constraints on allied forces, Pentagon officials said, two kinds of missions will remain under a separate American command: running prisons and counterterrorism operations to capture or kill high-value Taliban and Qaeda leaders. Many of those counterterrorism missions are classified, so it is not publicly known how many troops will remain under American command.  The command reorganization implies that an American officer will be in charge of the NATO and American missions for the foreseeable future.  The restructuring would also be intended to streamline the American-led training mission, which to a large extent has been outside the NATO structure.  But Pentagon and military officials said the new approach was crafted with attention to the sensitivities of NATO allies, and Mr. Gates and other officials consulted with the NATO secretary general, Jaap de Hoop Scheffer, and with the governments that have the largest number of troops in Afghanistan.  Mr. Gates has pledged that the United States will work to send up to two additional combat brigades to Afghanistan next year, a force that would number 6,000 to 10,000 troops.  Previously, the goal had been to expand the Afghan Army to 80,000 from 63,000 troops, and funds had already been allocated for that. The $20 billion will pay for the additional increase in soldiers.  Pentagon officials expect that they will need an estimated $5 billion per year for the first three years of the expansion, and then about $3 billion for each of the final two years of the expansion.  The United States will work with allies to help pay for the effort, Mr. Morrell said. Any new American money for the expanded Afghan Army, or proposals to divert money currently in the budget to that effort, would have to be approved by Congress.  A version of this article appears in print on , on Page A1 of the New York edition with the headline: Gates Pushing Plan to Double Afghan Army. Order Reprints| Today's Paper|Subscribe
A $20 billion plan would aid the Afghan Army and restructure the military command of U.S. and NATO forces in response to a growing Taliban threat.