Fewer than 100 Syrian rebels are currently being trained by the U.S. military to fight the Islamic State group, a tiny total for a sputtering program with a stated goal of producing 5,400 fighters a year.

The training effort is moving so slowly that critics question whether it can produce enough capable fighters quickly enough to make a difference. Military officials said last week that they still hope for 3,000 by year's end. Privately, they acknowledge the trend is moving in the wrong direction.

On June 26, 2014, the White House said it was asking Congress for $500 million for a three-year train-and-equip program. It only got started in May, however.

That program, together with a more advanced but also troubled parallel effort to rebuild the Iraqi army, is central to the U.S.-led effort to create ground forces capable of fighting IS without involving U.S. ground combat troops.

The Syria initiative is seen more as a way of enabling moderate opposition forces to defend their own towns against the militants. Expectations for the Iraqis are much higher; the goal is to have them roll back IS and restore the Iraq-Syria border.

The main problem thus far has been finding enough Syrian recruits untainted by extremist affiliations or disqualified by physical or other flaws. Of approximately 6,000 volunteers, about 1,500 have passed muster and await movement to training camps in other countries. Citing security concerns, the Pentagon will not say exactly how many are in training. Officials said that as of Friday, the number was under 100 and that none has completed the program.

"We have set the bar very high on vetting," said Col. Steve Warren, a Pentagon spokesman.

Maj. Gen. Michael Nagata, the Central Command special operations commander who is heading the program, wants volunteers with more than a will to fight.

"We are trying to recruit and identify people who ... can be counted on ... to fight, to have the right mindset and ideology," and at the same time be willing to make combating IS their first priority, Defense Secretary Ash Carter told the House Armed Services Committee on June 17.

"It turns out to be very hard to identify people who meet both of those criteria," Carter said.

Many Syrian rebel volunteers prefer to use their training to fight the government of President Bashar Assad, the original target of their revolution. While IS has been a brutal occupant of much of their country, the rebels see the extremists as fighting a parallel war.

The screening does not end with their preferred target. Dozens who were initially accepted have been sent home during training or quit because of revelations about their background or other problems, according to two senior U.S. defense officials. They were not authorized to discuss details and spoke on condition of anonymity.

Jennifer Cafarella, a Syria analyst at the Institute for the Study of War, doubts the viability of the training program.

"It is simply difficult to acquire the number of Syrian rebels willing to participate in the training under current parameters," she said.

Abdul-Jabbar Abu Thabet, commander of Aleppo Swords Battalion, a moderate faction that is fighting both Assad's forces and IS, said he believes the Americans are more interested in recruiting Syrian army defectors than moderate rebels.

He said he would no longer give Americans the names of training candidates from his group, after having done so once and not receiving a U.S. response.

"The Americans are saying they want to train rebels to fight against Daesh only," he said by telephone from northern Syria, using the Arabic acronym for the Islamic State group. "The fighting should be against Daesh, the (Assad) regime and everyone who is against the revolution."

The Pentagon announced in May that it had begun training 90 recruits in Jordan, but it has refused to give details. Defense officials, however, said last week that training also is underway in Turkey. Eventually it is to be expanded to bases in Saudi Arabia and Qatar.

Each trainee is receiving a U.S. stipend of between $250 and $400 a month, with the amount set by their skill level, performance and leadership role, said a Pentagon spokeswoman, Navy Cmdr. Elissa Smith.

The Pentagon also is wrestling with how to support those who complete the training and are sent back into Syria. Also, there are questions about how to avoid having their U.S.-supplied arms fall into the wrong hands inside Syria.

"So these constraints that we put on ourselves, which are perfectly understandable, do progressively limit the number of inductees into the program," Carter told Congress. "And that's proving the thing that limits the growth of the program."

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said at the same House hearing that "within the next couple of months" the administration will have to decide what kinds of post-training support the Syrian rebels will receive. He said the Pentagon is considering several forms, including intelligence, communications, logistics and battlefield airpower.

U.S. officials have pointed to the Syrian Kurds' successes in the north as an example of what U.S. airpower can enable when coupled with a credible, reliable ground force. But it does not answer the question posed by Rep. Tammy Duckworth, D-Ill., to Dempsey.

When she asked him whether the rebel training program is worth continuing, he offered something less than a ringing endorsement.

"It's a little too soon to give up on it," Dempsey said.

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Associated Press writer Bassem Mroue in Beirut contributed to this report.