(CNN) -- Pentagon officials are considering a preliminary assessment by Gen. John Allen, commander of NATO's International Security Assistance Force in Afghanistan, on "what he needs going forward" in the country as the U.S. looks to withdraw all combat troops by the end of 2014, a U.S. official tells CNN.
One of the options being considered is "to keep a force of roughly 10,000 U.S. troops in Afghanistan post-2014," according to the official who did not want to be identified discussing ongoing deliberations. The official said that force would comprise a small number of special operations forces dedicated to counterterrorism missions, while the remaining troops "would either continue to train and advise Afghan forces, or assist with logistical issues such as medical evacuations and air support operations."
The "10,000 option" is just one of several being examined, the official said. The options represented "different ends of the spectrum" in terms of troop levels, the official added, but the official did not provide any detail as to what those options are.
Defense Secretary Leon Panetta has not presented a formal recommendation to the White House, Pentagon spokesman George Little said on Monday.
"It's entirely premature to speculate on troop numbers in Afghanistan between now and the end of 2014 or beyond," he said. "In September, we completed the full withdrawal of the 33,000 surge troops, and we will soon begin considering how we move forward on further troop level adjustments, which will include planning for our post-2014 military and civilian presence in Afghanistan."
Panetta plans to speak with Allen about Afghanistan matters on Tuesday, Little said.
The ultimate decision is up to President Barack Obama, Little said.
"He receives options from our military leaders on the situation on the ground and considers the recommendations with his national security team, including [Panetta], in a consultation with the Afghan government and our international partners," he said.
Obama has not decided yet on troop levels after 2014, White House spokesman Jay Carney said Monday.
The U.S. official said the remaining troops "would need legal protection," a reference to any agreement that would grant troops immunity from being prosecuted under Afghan law. President Hamid Karzai has recently insisted that any remaining troops must be subject to Afghan law under certain circumstances. The potentially contentious issue was underscored by the case of Staff Sgt. Robert Bales, who is charged with 17 counts of murder in connection with a shooting massacre in an Afghan village.
But the U.S. official does not think the immunity issue will derail any potential deal, as it did in Iraq when a lack of agreement led to the U.S. pulling out all troops despite initial plans to keep several thousand there for advice and training.
"The Afghans know they really need our help," the official said. "President Karzai is strong enough to get a deal done. He is not as reticent to say 'we want a U.S. presence' as Prime Minister [Nuri al-] Maliki was in Iraq. It'll go down to the wire on immunity, but it won't be a deal-breaker."
Afghan National Security Forces officials acknowledge they will not have a viable air force until 2017 at the earliest and will need NATO airpower to sustain their missions.
A second U.S. official says the expectation going in is that "basing and money" will be two of the major issues to be worked out.
"The Afghans want to get as much money in the 'out years' as possible. Are we going to give them $6 billion a year for 20 years? Not likely. A five-year period is a safe bet, but the way appropriations work in Congress, we probably can't promise more than one year at a time in those later years," explained the second official.
The other major issue is what happens between now and the end of 2014. By May, new units are scheduled to replace up to eight Army brigade combat teams. The mission of the new "Security Force Assistance Brigades" will be primarily training and mentoring Afghan forces, not conducting combat operations. The new units are also about half the size of the brigades they will replace, reflecting the beginning of a smaller footprint in Afghanistan. They will deploy to areas in southern and eastern Afghanistan throughout the late winter and spring. These new training brigades will have their own security, transportation and logistics assets, so that they will not have to rely on other forces to conduct training.
Little said options for how to draw down troop levels in the coming year soon will be presented to the Defense Department. The president will make a decision on the pace of drawdown in the "coming weeks and months," Carney said.
The first U.S. official says there is "support" among some senior Pentagon officials to keep a majority of the 68,000 U.S. troops in Afghanistan through the fighting season in 2013. But he concedes that there is no consensus on that option and that it would require "moving away from a more gradual drawdown, as we've heard in the past, and bringing a lot of troops home quickly in 2014."