The top U.S. commander in Afghanistan said Tuesday that, once a scheduled 23,000 U.S. troops are withdrawn by the end of September, he does not expect to consider additional drawdowns until next year.

“I’ll give the president my best military advice with regard to the combat power that we’ll need to accomplish this mission, probably in 2013,” Gen. John R. Allen told Congress. “I’m not sure that I’d be able to see out to ’14 at that point, but I’d probably have a pretty good feel for it.”

The United States and NATO have agreed to withdraw all combat troops by December 2014. By then, the U.S.-led coalition will have transferred security authority to Afghan forces throughout the country, Allen said. “But we will still have combat forces in Afghanistan all the way to the end.”

Allen’s comments appeared to place a military marker in the path of the rapid withdrawal advocated by some lawmakers and, according to opinion polls, by a majority of the American public.

The question, which the administration has barely begun to discuss, is how fast to withdraw the 68,000 troops who will remain after September. During a news conference last week, President Obama called for a “gradual pace” that “doesn’t result in a steep cliff at the end of 2014.”

Allen and other commanders have indicated that they would prefer that all 68,000 troops remain through most of 2013 for an additional summer of fighting. Administration critics, including the leading Republican presidential contenders, have accused Obama of undermining the war effort by signaling withdrawal plans at all, of following the political winds in heading for an early exit, and of not listening to the advice of military commanders.

Rep. Howard P. “Buck” McKeon (R-Calif.), chairman of the House Armed Services Committee, asked Allen whether he had the administration’s assurances that “you can have the forces you believe you need through the end of the 2013 fighting season.”

In what appeared to be a carefully worded reply, Allen managed to be both pointed and respectful of presidential authority. “I have been given assurances by the White House that we’re in a strategic conversation,” he said. “There has been no number mentioned. There has been no number that has been specifically implied.”

So far, he said, the conversation has been “excellent,” and he is confident that any decision “will account for my recommendation, the recommendation of the theater commander, and the Joint Staff in this process.”

When McKeon asked whether the White House “has always followed your best military judgment,” Allen replied, “As the commander in Afghanistan, it has, sir.”

Allen gave a generally upbeat assessment of the war, saying that the United States is “on track” to achieve its military goals. The capabilities of Afghan security forces, he said, are “better than we thought” as they move toward assuming full security control.

“To be sure, the last couple of months have been trying,” Allen said. “None of us harbor illusions. We know that we face long-term challenges as well.”