U.S. Officials Debate Speeding Up Afghan Pullout Erik De Castro/Reuters American soldiers on patrol in Nangarhar Province this month. About 20,000 American troops are set to leave in September, but some officials want to pull out as many more by mid-2013. WASHINGTON - The Obama administration is discussing whether to reduce American forces in Afghanistan by at least an additional 20,000 troops by 2013, reflecting a growing belief within the White House that the mission there has now reached the point of diminishing returns. Accelerating the withdrawal of United States forces has been under consideration for weeks by senior White House officials, but those discussions are now taking place in the context of two major setbacks to American efforts in Afghanistan - the killings on Sunday of Afghan civilians attributed to a United States Army staff sergeant and the violence touched off by burning of Korans last month by American troops. Administration officials cautioned on Monday that no decisions on additional troop cuts have been made, and in a radio interview President Obama reaffirmed his commitment to the Afghan mission in spite of the recent setbacks, warning against "a rush for the exits" amid questions about the American war strategy. "It's important for us to make sure that we get out in a responsible way, so that we don't end up having to go back in," Mr. Obama said in an interview with KDKA in Pittsburgh. Any accelerated withdrawal would face stiff opposition from military commanders, who want to keep the bulk of the remaining American troops in Afghanistan until the end of 2014, when the NATO mission in Afghanistan is supposed to end. Their resistance puts Mr. Obama in a quandary, as he balances how to hasten what is increasingly becoming a messy withdrawal while still painting a portrait of success for NATO allies and the American people. The United States now has just under 90,000 troops in Afghanistan, with 22,000 of them due home by September. There has been no schedule set for the withdrawal of the remaining 68,000 American troops, although Mr. Obama said last year that the drawdown would continue "at a steady pace" until the United States handed over security to the Afghan forces in 2014. At least three options are now under consideration, according to officials at the White House, the Pentagon and the State Department. One plan, backed by Thomas E. Donilon, the national security adviser, would be to announce that at least 10,000 more troops would come home by the end of December, and then 10,000 to 20,000 more by June 2013. Vice President Joseph R. Biden Jr. has been pushing for a bigger withdrawal that would reduce the bulk of the troops around the same time the mission shifts to a support role, leaving behind Special Operations teams to conduct targeted raids. Mr. Biden has long said that the United States mission in Afghanistan is too broad and should focus primarily on a narrow counterterrorism mission against insurgents seeking to attack the United States. Mr. Obama's military commanders, meanwhile, want to maintain troops in Afghanistan as long as possible. If cuts have to be made, the commanders favor making them at the end of 2013, after the fighting season is largely finished. Any troop cuts made midyear would mean that those forces would not be available during the main fighting season, which runs from spring to early fall. "We've come up with several options, but they're back-of-the-envelope options," said a senior military official, who said the internal discussions were just now beginning to focus on the costs, logistics and security risks of each plan. Additional troop reductions would be consistent with a shift in mission that Mr. Obama plans to announce at a meeting of NATO members in Chicago in May. Under this plan, American troops would step away from the lead combat role to a supporting mission focused primarily on counterterrorism and training Afghan security forces. Mr. Obama will not announce the next troop reduction at the NATO meeting, aides said on Monday, but the size of the reduction will flow from the NATO decision on when to shift the mission in Afghanistan from combat to support. In his news conference last week, Mr. Obama called the goal for the NATO meeting to make "sure that the transition is not a cliff, but that there are benchmarks and steps that are taken along the way." Benjamin J. Rhodes, one of the president's senior national security advisers, said in an interview on Monday that "the trajectory we've set here is one of transition and Afghan sovereignty." He added, "We have a goal here of having the Afghans move into the lead and having us steadily pulling back." Once the United States and its allies agree on the timing for the shift in mission - Defense Secretary Leon E. Panetta has already said that it will take place as early as mid-2013 - the administration must decide exactly when the remaining 68,000 troops will come home. Already, debate there has fallen along familiar lines, according to the officials. Reporting was contributed by Alissa J. Rubin, Matthew Rosenberg, Graham Bowley and Rod Nordland from Kabul, Afghanistan, and by Elisabeth Bumiller en route to Kyrgyzstan.