Most of a US force sent by President Barack Obama to Afghanistan will stay in place through next year's "fighting season," Defense Secretary Leon Panetta said Thursday, as commanders push to keep troops on the ground as long as possible.

Panetta told lawmakers that 10,000 troops would be out as planned by the end of the year with the remaining 23,000 to remain deployed through next summer.

"We've already taken down by the end of this year the first 10,000 of the surge that was put in," he told the House Armed Services Committee.

"We'll take out the remaining part of that surge next year, by the end of the fighting season," he said.

The Pentagon chief did not specify precisely when troops were supposed to come home as the "fighting season" can last beyond September, but Obama has pledged to bring home the American forces by the end of September 2012.

Panetta's remarks came as top officials and military officers have raised the possibility of a future US military role beyond a planned withdrawal date of December 2014.

The Pentagon chief's comments on the drawdown of reinforcements appeared in line with a proposed plan by the top US and NATO general in Afghanistan, General John Allen.

Allen told ABC television in a recent interview that he wanted to put off the withdrawal of the surge troops as long as possible to reap the benefits of the additional manpower.

"They are going to stay a long time," Allen told ABC News. "Well maintain that number as long as we can."

Allen said he would probably request a logistical task force that would arrive in September to help bring out the remaining troops.

"As long as I can hold them, we will bring them out at the last minute, and fly them out of the theater and the logisticians, this group of logisticians, this task force will move their equipment out of the theater," he said.

In December 2009, President Barack Obama ordered a "surge" of 33,000 troops in a bid to turn the tide in the war against Taliban insurgents and in June this year, he promised to bring home the reinforcements by the end of September 2012.

US and NATO-led troops plan to gradually hand over to Afghan security forces over the next three years, and aim to withdraw all NATO-led combat troops by the end of 2014.

US officials and senior officers, however, have suggested the possibility of a future American military presence after 2014, albeit much smaller than the current force of about 98,000.

In a speech on Tuesday, Panetta said a US military contingent may be needed to prevent a resurgence of Al-Qaeda militants, most of whom fled to Pakistan at the outset of the ten-year-old war.

"We must build an enduring relationship with Afghanistan, to potentially include a military presence to maintain pressure on Al-Qaeda and its affiliates, and to ensure we continue to deny them safe havens," he said at the Woodrow Wilson Center in Washington.

Allen also said he expected a post-2014 mission.

"We are probably going to have some military presence in Afghanistan for some period of time... beyond 2014," he said.

A follow-on force likely would include trainers, combat support troops and special operations forces to counter Al-Qaeda and allied militants, he said.

The size and role of any future US military mission is currently under negotiation as US and Afghan officials hammer out the details of a long-term security pact.