The anticipated policy reversal reflects the U.S. embrace of Afghanistan's new and more cooperative president, Ashraf Ghani, and a desire to avoid the kind of collapse of local security forces that occurred in Iraq after the U.S. pull-out there.

It coincides with new efforts backed by Pakistan and China for peace talks between the Afghan government and the Taliban. Washington has welcomed greater engagement by China, which has helped create a diplomatic opening for reconciliation.

The U.S. official said conditions had changed since May when President Barack Obama declared that by the end of 2015 the U.S. force would be roughly halved from the current total of about 10,000 and would operate only from bases in Kabul and Bagram.

The White House had no immediate comment on the possibility of maintaining the Kandahar and Jalalabad bases into next year.

Obama is expected to decide in the next few days whether to slow the pace of the U.S. troop withdrawal, possibly by next week when Ghani and Afghan Chief Executive Abdullah Abdullah travel to Washington.