As it draws down troops in Afghanistan, the United States plans to rely heavily on its special forces, gambling the elite troops can serve as a firewall to prevent the Taliban seizing back power, experts and officials say.

Having backed a major troop buildup when he entered office, President Barack Obama is shifting course, opting for a scaled back military presence built around 9,000 special operations forces focused on training Afghan troops and striking insurgent leaders, officials said.

"It's a natural progression," said one defense official, who spoke on condition of anonymity.

"As the mission becomes more focused on training, it makes sense that special forces take on more importance. Training is one of their primary missions. That's what they do."

The approach reflects lowered expectations about what can be accomplished after ten years of war and carries an array of risks, analysts and former officials said.

"It's a policy calculation that these (conventional) troops won't be needed. I would bet there would be some challenges," said Jeffrey Dressler, an analyst at the Institute for the Study of War.

Obama's initial strategy was to knock back the insurgency in strategic areas in the south and east, gaining the upper hand on the battlefield to pave the way for handing over security to the Afghans and possible peace talks.

But while the Taliban lost ground in the south, NATO-led forces have yet to roll back the insurgents in the east and the war is still widely seen as a stalemate.

"The military mission is not complete," said Seth Jones of the RAND Corporation, a former adviser to special forces commanders.

A smaller NATO military footprint could allow the Taliban to gain back lost ground on the battlefield, especially in the southern Helmand province, possibly undermining Kabul's bargaining power in any peace talks with the insurgency, he said.

Obama's wager, however, has a chance of succeeding if the military aim is much narrower -- to avert disaster instead of fighting the Taliban in every corner of the country, Jones said.

"The only way this is likely to work is if the objectives begin to change," Jones said.

"If the US objectives are to prevent the Taliban from overthrowing the Kabul government, that may be something that is achievable."

Already, the United States no longer expects the central government in Kabul to provide security in every area. Instead, the US military has built up local police forces, leaving it to towns and villages to fend off the insurgents, he said.

It remains unclear how the drawdown of most coalition troops by the end of 2014 will affect the morale of Afghan forces as well as the West's uneasy relations with Afghan President Hamid Karzai.

Deploying and supplying special forces will require continued cooperation from the Afghan government, which harbors deep distrust of the special forces due to aggressive night raids and assaults that have claimed civilian lives.

If US economic aid and financial support for Afghan forces declines dramatically, Karzai and other leaders may choose to provide less than full cooperation to the Americans, said Stephen Biddle of the Council on Foreign Relations.

"The special forces' presence in particular has been quite controversial for Afghans," Biddle said.

"We sort of assume that we can withdraw all sorts of other things that the Afghans want, and they'll still give us what we want," he said. "One needs to think carefully about the sustainabilty of that."

By relying on a limited troop presence and special forces, the US approach has come full circle, resembling the model employed at the outset of the war by former president George W. Bush and his controversial defense secretary, Donald Rumsfeld.

Unlike the Rumsfeld era, fiscal pressures are partly driving the latest emphasis on a light footprint.

Circumstances in Afghanistan also are markedly different from 2001-2002, when the Taliban were in disarray, before the Islamist militants rebounded as a formidable insurgency.

"The problem now is without a sizable counter-insurgency effort, can the (Kabul) government persist in the face of a large, capable insurgency that did not exist in 2002?" Biddle said.