Officials offer varying views following U.S. Defense Secretary Leon Panetta’s Wednesday statement on ending combat in Afghanistan in 2013. (Jacquelyn Martin/AP)

U.S. and NATO officials struggled Thursday to clarify how long their troops would remain engaged in combat in Afghanistan amid disagreements over when and how Afghan security forces would assume that role.

Defense Secretary Leon E. Panetta said there was a consensus among NATO leaders that the fledgling Afghan army “will be ready to take the combat lead in all of Afghanistan” next year, with U.S. and NATO forces shifting to an advisory and training mission. British and French officials said they backed that idea, but other NATO officials were less definitive.

At a news conference at the alliance’s headquarters in Brussels, NATO Secretary General Anders Fogh Rasmussen said “we don’t know yet” when newly trained but inexperienced Afghan forces — who now number more than 300,000 — will take charge of the combat mission in the war. He predicted that NATO would resolve the issue at its summit in Chicago in May.

Rasmussen said that NATO forces would remain actively engaged in combat until the end of 2014, when most allied troops are scheduled to withdraw from Afghanistan. “Let me stress,” he said, “we will conduct combat operations throughout that period.”

On Wednesday, while en route to Brussels, Panetta surprised some allies by saying that the Obama administration wanted to shift from “a combat role to a training, advise and assist role . . . hopefully by mid- to the latter part of 2013.”

That timeline would represent an acceleration in NATO’s plans.

On Wednesday, Panetta acknowledged that U.S. troops could still be involved in combat after 2013 but indicated that they would fight only to protect themselves.

On Thursday, however, he modified that characterization, saying U.S. forces would still regularly engage in combat but in a “support role.”

“It’s basically, the Afghans themselves will be in charge of combat operations,” he told reporters. “Again, we’ll be there for support; we’ll be there for guidance. But they’re the ones that are going to be in the lead and conduct the operations.”

It was unclear what those changes would mean on the battlefield.

Asked to elaborate on the difference between a “lead” combat role and a “supporting” role, a senior U.S. defense official said that American troops would perhaps remain embedded with Afghan forces. But the official, who spoke on the condition of anonymity, said the questions of who would issue orders and how tactical duties would be divided had not been resolved.

Another senior NATO official, also speaking on the condition of anonymity to discuss internal deliberations, said no decision had been reached about when the Afghans would take over combat duties. But the NATO official had difficulty squaring that with Panetta’s comments.

“He said the combat role will come to an end” in 2013, the official said of Panetta. “But he also said combat will continue. And that’s exactly what I’m saying.”

Anthony H. Cordesman, an influential military analyst at the Center for Strategic and International Studies in Washington, criticized the Obama administration for lacking a clear plan for winding down the war.

“The practical problem is that [Panetta] did not define what he meant,” Cordesman wrote Thursday in an online commentary. “It is easy to talk about a transfer of responsibility to the Afghans, but as a similar statement in Iraq showed, this can be little more than cosmetic or be based on real Afghan capabilities.”

In Washington, exasperated officials insisted that Panetta’s comments had been misinterpreted and that there was no change in plans for Afghanistan.

CIA Director David H. Petraeus, a former Army general who commanded U.S. and NATO troops in Afghanistan until last summer, told a congressional panel that Panetta’s remarks had been “over-analyzed.”

Current NATO policy calls for Afghan security forces to gradually assume the lead role in combat actions before the withdrawal of all coalition combat troops by the end of 2014, officials said.

“That is the policy, and that has not changed,” White House spokesman Jay Carney said.While U.S. and NATO combat troops will remain in Afghanistan for the next three years, in still unspecified numbers, Afghan troops have already taken the lead in some areas and could complete the transition, with ongoing coalition support, well before that, he said.

The end of that process “could be moved up to 2013,” Carney said, depending on conditions on the ground and consultations within NATO. Panetta, he said, “was not making an announcement about a decision that was made, but about consultations that will be taking place.”

Staff writer Karen DeYoung in Washington contributed to this report.