A rebel fighter readies a mortar during clashes with regime forces in the northern Syrian city of Aleppo on October 31, 2014. Syria accused Turkey on October 30, of a "flagrant violation" of its sovereignty, as Ankara allowed Iraqi Kurdish peshmerga fighters and opposition rebels to cross its border to battle jihadists. AFP PHOTO/KARAM AL-MASRIKARAM AL-MASRI/AFP/Getty Images (Karam Al-Masri/AFP/Getty Images)

The Obama administration has been weighing plans to escalate the CIA’s role in arming and training fighters in Syria, a move aimed at accelerating covert U.S. support to moderate rebel factions while the Pentagon is preparing to establish its own training bases, U.S. officials said.

The proposed CIA buildup would expand a clandestine mission that has grown substantially over the past year, U.S. officials said. The agency now vets and trains about 400 fighters each month — as many as are expected to be trained by the Pentagon when its program reaches full strength late next year.

The prospect of expanding the CIA program was on the agenda of a meeting of senior national security officials at the White House last week. A White House spokesman declined to comment on the meeting or to address whether officials had reached a decision on the matter.

Others said the proposal reflects concern about the pace of the Pentagon’s program to bolster moderate militias, which so far have proved no match for al-Qaeda offshoots including the Islamic State.

“We need a little more urgency in helping the moderates, and the agency was viewed as the best way to get that going fast,” said a senior U.S. official, who spoke on the condition of anonymity, citing the sensitivity of the Syria debate.

A decision to expand the CIA program would deepen U.S. involvement in Syria, where the United Nations says 200,000 people have been killed during more than three years of civil war. The agency’s mission is a central but secret component of a broader U.S. effort that also involves airstrikes and an influx of U.S. military advisers into Iraq.

The agency’s ability to scale up its operation over the past year has given officials confidence that U.S. teams can recruit and screen larger numbers of fighters without increasing their exposure to security risks including infiltration by al-Qaeda.

Even so, there is little indication that U.S.-trained and armed moderates have had any substantial impact on the direction of the conflict in Syria.

The latest setbacks came this month, when CIA-backed factions were routed by Jabhat al-Nusra, al-Qaeda’s primary affiliate in Syria. Fighters with militias including Harakat Hazm — one of the biggest recipients of U.S. arms — fled positions in towns across northern Syria, with many leaving their weapons to be scooped up by al-Nusra.

Rep. Adam B. Schiff (D-Calif.), a member of the House Intelligence Committee, said the ease with which those groups were overrun exposed problems that will be difficult to offset through remote training, even if it is ramped up.

Scenes of “the moderate opposition either melting away, running away or joining league with al-Nusra is a good indication of the difficulty that we’re going to have,” Schiff said. He would not discuss classified programs but said he has been troubled by other recent developments including the outrage voiced by supposed moderate factions over U.S. airstrikes that hit al-Nusra positions, suggesting that U.S.-backed militias see the al-Qaeda affiliate as an ally against Syrian President Bashar al-Assad and not as an adversary.

The CIA declined to comment on any aspect of its role in Syria.

The agency’s training effort began early last year after President Obama issued a classified “finding” that authorized the CIA to start providing arms and instruction to beleaguered insurgents seeking to oust Assad.

Initially, the program was run from secret camps in Jordan, but over the past year, it has expanded to include at least one location in Qatar, according to U.S. and Middle East officials. Much of the instruction is carried out by U.S. commandos working on loan from the Department of Defense.

Fighters have been drawn from militias in Syria as well as refu­gee camps. The intelligence services of Saudi Arabia, Jordan and other regional U.S. allies have been involved in the training as well as assisting in background checks to help ensure that combatants with ties to al-Qaeda are excluded.

The agency has collected biometric data on fighters who pass through the program, officials said, meaning DNA samples, iris scans or other identification markers. The weapons distributed have been mostly light arms, although Harakat Hazm was among a select group of units to be given U.S.-made TOW antitank missiles.

Overall, the CIA is operating on pace to train about 5,000 fighters a year — roughly the same output that Pentagon officials have said they aim to achieve.

Defense Secretary Chuck Hagel testified this week on Capitol Hill that preparations for the Pentagon training program are now “complete,” and that “Saudi Arabia, Turkey and other partner nations have agreed to host training sites.”

But recruiting and vetting will not begin until Congress authorizes funding, Hagel said, adding that it would take eight to 12 months “to begin making a difference on the ground.”

Acceleration of the CIA training program could help compensate for that delay. It could also address an imbalance in Obama’s strategy that involves thousands of U.S. military personnel in Iraq to help that country’s military regroup but no comparable ground force to work with in Syria.

U.S.-led airstrikes began early in the summer after major Iraqi cities including Mosul were overrun by the Islamic State, a group that severed ties with al-Qaeda last year, declared a border-straddling caliphate and made propaganda videos of its executions of U.S. and British citizens.

The group’s haven in Syria is seen by U.S. intelligence officials and military planners as one of the main obstacles to Obama’s declared aim to “degrade and eventually destroy” the Islamic State.

Months of airstrikes have slowed the Islamic State’s momentum but have not dislodged it from strongholds in the Syrian city of Raqqah and elsewhere. U.S. defense officials have outlined a goal of assembling a force of up to 15,000 whose main objective will not be fighting Assad but gradually prying territory away from the Islamic State.

U.S. officials said their vetting efforts will focus on identifying recruits who are willing and motivated to fight the Islamic State, but they acknowledge that enforcing that agenda may prove difficult once the fighters leave CIA and U.S. military camps.

“There’s going to be fighting in Syria that we cannot necessarily predict,” retired Marine Corps Gen. John R. Allen, the administration’s coordinator for the Syria and Iraq coalition, said in an interview with Al Jazeera last month. The hope, he said, is that U.S.-trained forces will be able to hold their own against Assad’s military, al-Nusra and other groups but will focus their offensive operations against the Islamic State.

“We are dealing with that component first because we must,” Dempsey said. “They’re a threat to our allies. They are a threat to us.”

Missy Ryan contributed to this report.