Gerald Herbert, Associated Press
Gen. Stanley McChrystal, left, Commander of the International Security Assistance Force and Commander of U.S. Forces in Afghanistan, arrives to testify with U.S. Ambassador to Afghanistan Karl W. Eikenberry, right, before the House Armed Services Committee on Capitol Hill in Washington Tuesday.

WASHINGTON — The general in charge of the war in Afghanistan said Tuesday he expects to know by this time next year whether the new troop buildup is reversing Taliban momentum and he believes he will be able to draw down forces in 2011 without asking for more.

Gen. Stanley McChrystal, appearing before House and Senate panels a week after President Barack Obama announced his new surge-and-exit strategy, said he had not recommended the 18-month expiration date for the surge that Obama applied and would have preferred more forces than he is being given. Still, he supported the plan without reservation.

"I'm comfortable with the entire plan, sir," McChrystal told a skeptical Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee.

Ambassador Karl Eikenberry, who had voiced misgivings previously, also saluted the new approach.

The two men sat side by side at a pair of Capitol Hill hearings long sought by Republicans critical of the lengthy White House review that yielded the decision to send an emergency infusion of 30,000 additional U.S. forces. Although they took pains to say they are friends, they displayed none of the hand-in-glove unity of the Gen. David Petraeus and U.S. ambassador Ryan Crocker, who managed the Iraq surge nearly three years ago.

Sen. John McCain, the senior Republican on the panel, pointedly told the men he hopes that any differences they have are put to rest. He praised the decision to send additional U.S. forces but said the deadline to begin bringing them home is a mistake.

"We have announced a date divorced from conditions on the ground," McCain said.

The new battle strategy includes a plan to begin bringing some troops home in 18 months. How many troops leave would be determined by conditions on the ground at that time.

"Results may come more quickly," McChrystal told lawmakers. "But the sober fact is that there are no silver bullets. Ultimate success will be the cumulative effect of sustained pressure."

Eikenberry said the course outlined last week by Obama "offers the best path to stabilize Afghanistan and to ensure al-Qaida and other terrorist groups cannot regain a foothold to plan new attacks against our country or our allies."

Rep. Ike Skelton, D-Mo., chairman of the House Armed Services Committee, said Obama did the right thing by ordering an additional 30,000 U.S. troops. But he opened the hearing by ticking off a series of questions, asking what success will look like, how it will be measured, "what risk are we accepting in the next 18 months and how can we mitigate it?"

McChrystal assured Skelton that the troop infusion will work. "I believe we will absolutely be successful," the general said.

The House panel's highest-ranking Republican, Rep. Howard "Buck" McKeon of California, told McChrystal he was waiting to hear how "the president is not under-resourcing his own strategy," since the general has sketched ways that as many as 80,000 additional U.S. forces could have helped turn the tide.

Under questioning later from McKeon, McChrystal said he did not think he would need to ask for any more troops in a year's time, but would not hesitate to recommend more if circumstances change.

He also told McKeon he did not recommend the July 2011 exit plan, but that he supports it. He said he made no recommendations at all about the exit plan.

"By the summer of 2011, it will be clear to the Afghan people that the insurgency will not win, giving them the chance to side with their government," McChrystal said. "From that point forward, while we begin to reduce U.S. combat force, levels, we will remain partnered with the Afghan security forces in a supporting role to consolidate and solidify their gains."

Visiting Afghanistan on Tuesday, Defense Secretary Robert Gates reiterated that the administration expects the withdrawal, beginning in July 2011, to be "a several-year process — whether it's three years or two years or four years remains to be seen."

Afghanistan President Hamid Karzai said his country will need international help to build homegrown security forces well beyond that date. "For a number of years, maybe for another 15 to 20 years, Afghanistan will not be able to sustain a force of that nature and capability with its own resources," Karzai said during a joint news conference with Gates in Kabul.

In Washington, Eikenberry sought to clarify his stance during the three-month review, widely-reported as a hesitancy to support more troops at a time when there were still so many questions surrounding the corruption and mismanagement that have stained the Karzai administration.

"It was not a question of additional troops," he said. "It was a question of the number of troops ... the timelines... the context that those troops would operate in."

Asked what his biggest challenges will be, McChrystal said growing the Afghan security forces in size and quality, bolstering the quality of Afghan government and convincing the Afghan people to support their government even as they are being "coerced by the Taliban."

McChrystal predicted improvement in Afghan security forces, who eventually must take responsibility for protecting their own country.

"My expectation is the insurgency will be less robust in the summer of 2011, significantly so, and my expectation is that the Afghan national security forces will be more robust," McChrystal said, although "still imperfect."