WASHINGTON -- Republicans looking for a political opening to challenge President Barack Obama on national security got little help Tuesday from the top military commander in Afghanistan, who insisted that the White House is heeding his advice.

In his much-anticipated appearance before Congress, Marine Gen. John Allen said shifting the security responsibility from U.S. and coalition troops to Afghan forces is on track more than 10 years after the Sept. 11 terrorist attacks and after more than a decade of war. The ongoing conflict has divided Congress and increased the public demand to bring the 90,000 U.S. troops home, a call that grew louder in recent weeks after burnings of Qurans and a shooting spree that killed 16 Afghan civilians stoked anti-American rage.

The current plan calls for the U.S. to withdraw its surge force of 23,000 American troops by the end of September, with a complete drawdown by December 2014. Allen told the House Armed Services Committee that he would assess the insurgency threat and the progress of coalition forces later this year before recommending the pace of future withdrawals -- a step that pushes that decision past the November elections.

Republicans repeatedly pressed Allen on whether the White House, facing election-year pressure to speed up the drawdown, was at odds with the military commanders, dictating the mission or the size of the U.S. force. Republicans hope to challenge the Democratic commander-in-chief on national security issues, but the killing of terrorist leader Osama bin Laden, a weakened al-Qaida and the end of combat operations in Iraq have given the GOP limited opportunities to criticize Obama.

The president gets high marks in public opinion polls on national security.

Focusing on the narrative that Obama isn't listening to his commanders, Rep. Mike Conaway, R-Texas, questioned what Allen would do if the administration announces, without his input, what the size of the U.S. force in Afghanistan should be.

"I've been given no indications that there is a number that will ultimately be detailed to me to build a strategy around," Allen said.

One exchange with the chairman of the Armed Services panel, Rep. Howard "Buck" McKeon, R-Calif., underscored that Allen and his commander in chief were speaking from the same page at this stage in the conflict.

"Have you been given assurances by the White House that you can have the forces that you believe you need through the end of the 2013 fighting season?" McKeon asked.

"I have been given assurances by the White House that we're in a strategic conversation, chairman. There has been no number mentioned. There has been no number that has been specifically implied," Allen said. "There's an excellent, I believe, strategic conversation that is going on, that will account for my recommendation, the recommendation of the theater commander, and the Joint Staff in this process. And I'm very pleased, frankly, with where we are in that conversation now."

"Has the White House always followed your best military judgment?" McKeon asked.

"As the commander in Afghanistan, it has, sir," Allen said.

Allen's appearance before the committee -- he testifies in the Senate on Thursday -- comes after major setbacks to the fragile U.S.-Afghanistan relationship. The Quran burnings touched off protests and riots that left 32 Afghans dead. Seven Americans were killed, apparently by Afghan forces. More recently, the massacre of 16 Afghan civilians, allegedly by a U.S. soldier, inflamed the anti-American sentiment.

In response, angry Afghan leaders demanded that U.S. troops pull out of local villages and rural areas.

Allen said that the U.S. and its coalition forces are moving ahead in to ensure that Afghanistan doesn't revert to a terrorist haven and transfer the security lead to the Afghans. The forces, he said, are meeting the commitments spelled out in the overall withdrawal plan hammered out at the conference in Lisbon in November 2010.

In the past year, Afghan security forces have expanded from 276,000 to 330,000 and will achieve their goal of full strength before an October deadline. He said eventually Afghans will take the lead of night raids.

"Throughout history, insurgencies have seldom been defeated by foreign forces. Instead, they have been ultimately beaten by indigenous forces," Allen said. "In the long run, our goals can only be achieved and then secured by Afghan forces. Transition, then, is the linchpin of our strategy, not merely the way out."

At the White House, presidential spokesman Jay Carney said he did not expect a withdrawal timeline to emerge from a much-anticipated NATO summit in May in Chicago even though Afghanistan will dominate the gathering. Obama has offered no specifics on when the next troops will come home, other than to promise a gradual withdrawal.

In his opening statement, McKeon was critical of Obama.

"In the absence of sustained, public campaign to support the mission in Afghanistan -- from the White House on down -- many have begun to question what we're fighting for," the chairman said. "With friend and foe alike knowing that the U.S. is heading for the exits, our silence is likely viewed as a preamble to retreat. And, in warfare, when the mission becomes redeployment, rather than mission success, the outcome can quickly become disorderly."

At a news conference following the hearing, McKeon said Obama should use his "great bully pulpit" to explain Afghanistan to the American people.

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Associated Press writer Lolita C. Baldor contributed to this report.