Rebel fighters run during a battle against Syrian government soldiers in Handarat, on Oct. 20. Moderate Syrian fighters have been deemed essential to defeating the Islamic State under the Obama administration’s strategy. (Fadi Al-Halabi/AFP/Getty Images)

The Syrian opposition force to be recruited by the U.S. military and its coalition partners will be trained to defend territory, rather than to seize it back from the Islamic State, according to senior U.S. and allied officials, some of whom are concerned that the approach is flawed.

Although moderate Syrian fighters are deemed essential to defeating the Islamic State under the Obama administration’s strategy, officials do not believe the newly assembled units will be capable of capturing key towns from militants without the help of forward-deployed U.S. combat teams, which President Obama has so far ruled out. The Syrian rebel force will be tasked instead with trying to prevent the Islamic State from extending its reach beyond the large stretches of territory it already controls.

“We have a big disconnect within our strategy. We need a credible, moderate Syrian force, but we have not been willing to commit what it takes to build that force,” said a senior U.S. official involved in Syria and Iraq operations who, like others cited in this report, spoke on the condition of anonymity because he was not authorized to discuss the training program.

Military commanders are reluctant to push Syrian fighters into full-scale battles with well-armed militants if they cannot summon close air support and medical evacuations, mindful of how fledgling forces in Iraq and Afghanistan crumbled without that assistance during the early years of the wars in those nations. But U.S. military aircraft cannot provide that aid without American or allied troops in close proximity to provide accurate targeting information on secure radio channels.

Military officials also want U.S. and allied special operations troops to advise opposition forces if those forces are thrust into combat, helping them to fight effectively and reducing the chances that the new units will disintegrate in the heat of battle.

“You cannot field an effective force if you’re not on the ground to advise and assist them,” said a senior U.S. military officer with extensive experience in training the Iraqi and Afghan militaries.

Obama’s unwillingness to deploy ground combat forces is rooted in concern that American troops would be drawn into a long, bloody war in the Middle East.

In announcing the campaign to confront the Islamic State, the president said the United States would “strengthen the opposition as the best counterweight to extremists.” The Pentagon subsequently announced that the U.S. military would seek to train as many as 5,000 Syrian fighters a year, aiming to build what Defense Secretary Chuck Hagel called an “effective opposition force, not just a hit-and-run group of rebels.”

The Obama administration’s plan calls for U.S. Special Operations troops to recruit moderate Syrian opponents of the Islamic State from refugee communities in Jordan, Turkey and other nations. They will be flown to Saudi Arabia, trained for about eight weeks, and then sent into the small enclaves of Syria already controlled by the Free Syrian Army and other moderate opponents of the Islamic State. The first units are expected to be deployed in roughly six months.

“The plan is for them to safeguard cleared areas,” said a senior official of an Arab nation that is part of the U.S.-led coalition and who has been briefed on the training program. “They will end up being a defensive force more than an offensive force.”

Lt. Gen. William Mayville, the director of operations for the Pentagon’s Joint Staff, said the opposition fighters would receive “basic training to secure their villages.” The force, he said, “will have some effect,” but he acknowledged that the fighters “won’t have the decisive effect” in the battle against the Islamic State.

A defensive opposition force also could allow President Bashar al-Assad’s government to regain territory it has lost to the Islamic State, which has been pummeled — but remains far from defeated — by hundreds of U.S. and coalition airstrikes over the past month.

The administration has made little secret of the fact that reversing Islamic State gains in Iraq is the primary goal of its military strategy in the region. Airstrikes in Syria, senior administration officials have said, are not designed to push out the militants but to destroy the infrastructure, sources of revenue and command structure that have enabled them to operate successfully in Iraq.

Those officials maintain that it is premature to focus on the question of whether U.S. advisers should deploy with the new Syrian force. A more pressing concern, they contend, is the challenge of recruiting willing, competent fighters from Syrian refugee communities. U.S. officials do not want to pull away members of the Free Syrian Army who already are fighting in Syria, but they worry that many of those who have fled the country as refugees may not want to return to their war-ravaged homeland.

The officials said they intend for U.S. troops to use the basic training sessions, which will focus on unit discipline and elementary combat skills, to identify promising candidates for more advanced courses. Those individuals could be schooled to engage in more offensive missions.

“We will evolve and learn as the program proceeds,” said a senior Defense Department official. For now, the official said, “there is an enormous focus on building leadership structure.”

The first phase, Mayville said, “is identify and vet them, create a relationship and give them basic training.” Then, he said, they will “go back and protect their communities.”

Thus far, senior military leaders have concurred in public with Obama’s decision not to send ground combat troops to Syria and Iraq, but the country’s top military officer, Gen. Martin Dempsey, has said that if he determines that it is necessary for U.S. advisers to accompany local forces on attacks against Islamic State targets, he would make such a recommendation to the president.

Administration officials say technological advancements will allow the U.S. military to provide a degree of air support to Syrian forces without having to stand shoulder to shoulder with them. They note that in Iraq, U.S. commanders recently employed surveillance aircraft, including drones, to identify Islamic State militants near the Mosul Dam, striking them in proximity to Kurdish forces.

But military officials regard those Kurdish forces as far more seasoned than the newly assembled Syrian fighters will be. “This isn’t just about coordinating airstrikes,” the senior military officer said. “It’s about keeping up morale, attending to injuries, ensuring order within the ranks. You can’t do that from afar.”

U.S. officials are talking to the governments of Jordan, Qatar and Turkey about opening additional training camps in those nations, should the volume of recruits exceed capacity in the two facilities that are being established in Saudi Arabia.

Skeptics of the administration’s policy within the Pentagon and in Congress worry that the recruitment effort will be hindered by a lack of a clear U.S. commitment to assist the new force. They also argue that the administration’s unwillingness to commit to toppling Assad — Obama has said he wants to see a “political solution” to the civil war in Syria — will lead many moderate opponents to sit on the sidelines.

“It’s immoral to ask these young men to fight and die when we’re not going to protect them from Bashar Assad’s barrel bombs or from ISIS,” said Sen. John McCain (R-Ariz.), a member of the Senate Armed Services Committee, referring to the Islamic State by a common acronym. “You’re not going to get people to volunteer to do that.”

The senior Defense Department official said the administration is “committed to making sure these forces succeed.” Other officials said those steps could involve the use of covert operatives and private contractors reporting to the CIA, not the Pentagon, who could provide combat advice to Syrian forces and summon air support. Another option under consideration is to ask Arab nations that have participated in airstrikes on Islamic State targets to send some of their special operations units to Syria.

But the senior Arab official said such a request would be unlikely to receive an enthusiastic response among coalition members if the United States did not also commit troops.