WASHINGTON - US President Barack Obama's plan to directly arm rebels fighting inside Syria is raising concern from Congress and intelligence officials over whether it provides enough safeguards to prevent the weapons falling into the wrong hands.The new approach replaces a largely failed effort in which the Pentagon trained rebels outside of Syria and sent them back to the battlefield after an exhaustive vetting process to ensure they were not linked to radical Islamic groups. Only about 180 rebels were trained, of whom 145 remain active, with about 95 inside Syria, a military spokesman said on Friday.The revised plan to battle Islamic State in northern Syria kicked off on Oct. 11, when US Air Force C-17 cargo planes conducted what the Pentagon described as a successful airdrop of machine gun ammunition, grenades and rocket-propelled grenade rounds to Syrian Arab fighters.The concerns stem from the fact that, under the new program, only rebel commanders - not individual fighters - will be screened, as well as the inherent risk of inaccuracy in airdrops to areas controlled by overlapping militant groups.Officials of several agencies involved in Syria policy and operations, along with Congressional oversight sources, said they had little confidence in the effectiveness of the Pentagon's procedures to vet the loyalties and credentials of Syrian rebels receiving US weapons. The US agencies are often unable to gather enough information to verify the rebels' identities, credentials and allegiances, the officials said.In a closed-door Congressional briefing on changes to the $580 million program, administration officials did not provide sufficiently detailed answers as to how vetting could be effectively carried out, one source familiar with the briefings said. The vetting procedures appeared to be "leaky," said the source, who spoke on condition of anonymity.Congressional intelligence and armed services committee spokespeople did not respond to requests for comment. Representative Adam Schiff, the senior Democrat on the House intelligence committee and who supports the plan, said it had the advantage of focusing on battle-hardened groups that Washington was already familiar with."But I think that the long history of this war has already demonstrated that you can only have so much confidence that any material support you provide is going to stay in the right hands," he said.One would "have to expect that some of that is going to bleed into groups that we don't want to equip," he added.The change in plan amounted to an about-turn for Obama, who in past years questioned the wisdom of sending more weapons into Syria's civil war. Obama's aides say that under the recalibrated Pentagon program, the leaders of Syrian units given arms will be rigorously screened, and that US military personnel are in contact with commanders on the ground.The Pentagon says it can communicate directly with the groups and monitor how the equipment is being used."Groups that maintain control over the equipment provided will be able to qualify for more and perhaps better equipment, while those that demonstrate an inability to keep control will lose support," said Col. Patrick S. Ryder, a spokesman for US Central Command, adding that "...we cannot completely eliminate risk."WRONG HANDS? Colonel Steve Warren, a Baghdad-based spokesman for the U.S.-led coalition battling Islamic State, said on Tuesday the weapons and equipment had been dropped to leaders of the Syrian Arab Coalition, a collection of 10 to 12 groups numbering about 5,000 fighters.The leaders had previously received US training outside the country for about a week, including on the law of land warfare and the use of communications gear.The weapons are coming from large stocks purchased for the original $580 million train-and-equip program, warehoused in the region, and now being directly diverted to the battlefield.The Pentagon told Congress in a June report that it had so far spent $136 million on weapons, ammunition and related material. Out of the $580 million, it said, a total of $367 million, or 74 percent, was earmarked for weapons and equipment.It is not only Islamic radical groups that critics of the plan fear could end up gaining US-supplied firepower.Turkey has registered unhappiness over the new plan, calling in the US ambassador last week to express concern that Washington's arms drops were aiding Syrian Kurdish militias. Turkey, which has its own large Kurdish minority, objects to empowering those militias, although they have been the most effective US-allied force against Islamic State in Syria.Pentagon spokesman Peter Cook told a news briefing last Thursday that Kurdish forces recovered some of the weapons from Sunday's airdrop. But he quickly corrected that statement, saying that only Syrian Arab fighters had received the arms. The Arab forces and the Kurdish YPG militia, however, coordinate on the battlefield.The YPG said on Oct. 12 it had joined forces with Arab rebels and that their new alliance has been promised fresh weapon supplies by the United States for an assault on Islamic State forces in what is effectively their capital, Raqqa.US intelligence sources' criticism could stem partly from competition: the CIA has been running a separate, ostensibly covert, program to train and arm Syrian rebels.Undersecretary of Defense Christine Wormouth told reporters when the policy switch was announced on Oct. 9 that the Pentagon had been working with groups on the ground for months and has "pretty high confidence in them already."Another way the Pentagon will mitigate the risk, Wormouth said, is by providing only basic weaponry, at least initially.