AMMAN, Jordan — Now that President Obama has decided to provide military assistance to Syrian rebels, the next step is not difficult, said a military analyst who's been studying the Syria conflict.

U.S. intelligence has vetted the rebel forces to determine who should get the arms, and it has a willing middleman in Turkey on Syria's northern border, said Christopher Harmer, an analyst with the Institute for the Study or War.

Turkey, a NATO member, has air bases and ports U.S. forces have used to move equipment and people to conflicts in Iraq and Afghanistan, he said.

Turkey's Incirlak Air Base, which is technically a NATO air base, is one likely hub for U.S.-supplied weapons intended for the rebels, Harmer said.

"The U.S. moves cargo through there all the time," Harmer said. Establishing a supply route to the rebels "is not that hard."

Tony Badran, an analyst with the Foundation for the Defense of Democracies, said Syrian troop movements toward the major rebel stronghold Aleppo could disrupt that well-worn supply route in Syria.

"It's a very important area for weapons supplies because it's close to the border with Turkey, and the countryside along the border with Turkey is really where all those weapons come in," Badran said.

The United States has been sending communication equipment to rebels of the Free Syrian Army through Turkey. Rebels have picked up shipments in Istanbul and driven them across the border into Syria along secure routes.

Turkey has sea ports for larger shipments. Most of the arms rebel leaders have requested are light weapons, chief among them shoulder-fired missiles. The missiles are wanted to shoot down Syrian aircraft or disable Syrian tanks.

If the United States agrees to provide such weapons, they can be delivered to Turkey by air, Harmer said. Arms could then travel by truck or rail to the Turkish border with Syria, and that's where U.S. control over the weapons will probably end, Harmer said.

The effort depends on Turkish cooperation. Turkish Prime Minister Recep Tayyip Erdogan has allowed weapons from Saudi Arabia and Qatar to move through his country, and he supports the toppling of Syrian President Bashar Assad's regime.

The Syrian rebels control at least 20 miles of Syrian territory south of the Turkish border, "so there's really no mechanical way for the Syrian government to stop them," Harmer said.

There is a risk that Syria will directly attack Turkey over the shipments. Syria has fired missiles into Turkish territory along the border to target weapons shipments and rebel fighters seeking protection. Turkey has hosted about 1 million Syrian refugees, and rebels have camps there as well.

The U.S. presence in Syria will probably be very small, limited to CIA or Special Forces operators, and focused on identifying rebel groups they can trust, Harmer said.

"We don't want to provide weapons to al-Qaeda affiliates" who are also fighting the government in Syria, he said.

When the conflict started, the rebels' identity and motivations were not well understood. Harmer said two years have changed that situation. The Institute for the Study of War and other independent groups have completed extensive studies on the various rebel groups.

"We know from open sources, YouTube videos and interviews who are secular freedom lovers and who are the extremist religious types," Harmer said.

Rebel leaders have reported Syrian government forces moving toward Aleppo, Syria's largest city in the north and a hub for rebel operations and supplies and fighters coming from Turkey.

The massing of troops for a possible offensive on Aleppo has led to "a major freakout" among rebel supporters about whether the divided city will fall to a combined assault by government forces and fighters from Hezbollah, the Iranian-backed Shiite militia in Lebanon, Badran said.

Assad used a combination of total siege, artillery bombardment and hundreds of Hezbollah ground forces to overtake Qusair last week after a battle that lasted almost a month, but that approach will be much more difficult in Aleppo, Badran said.

Rebels control most of the countryside between Aleppo and Turkey to the north, and activists on the ground report that the Turks have secured all the border crossings, in preparation for weapons shipments to start flowing, he said.

The timing of Obama's announcement provides political cover to other U.S. allies, such as the British, French, Turks, Qatar and Saudi Arabia that are poised to start supplying rebels in earnest, he said.

"To lock down Aleppo like the regime did in Qusair is not going to be as easy," Badran said.

The Free Syrian Army has been complaining over a lack of weapons since last year. What they mainly have is small arms and grenades taken from regime forces or smuggled through from Turkey, Jordan and Lebanon, sometimes paid for by Gulf states such as Qatar.

"A couple of countries have been doing that already through Turkey or Jordan," said Hozan Ibrahim, a Syrian opposition activist based in Berlin. "It is not an obvious cooperation, but they are doing that underground, undercover, and that is totally OK with us. And of course, in Turkey, there is the headquarters of the Syrian army."

Commanders say that as the conflict has dragged on, more regime soldiers have defected and foreign fighters have joined the battle, rebels' technical know-how has grown.

"At the beginning of the revolution, we used to buy arms from the regime's shabiha (thugs)," said Abu Jarah, leader of Al al-Bait Battalions in Binish-Idlib, part of the opposition forces. "The regime wanted to get rid of all its damaged arms, so they pushed them onto the streets.

"We used to buy them for high prices because our need to defend ourselves was urgent. Meanwhile, they used that money to buy advanced, more lethal weapons. After that, some traders in Aleppo assisted us through Turkey, Lebanon and the Jordanian borders near Daraa.

"Now, we've started to manufacture and develop our own weapons," he said. "The Syrian people get the means to defend themselves any way they can."

Still, shortages are everywhere, and the FSA needs help. Qatar money has been drying up, and as Hezbollah has become increasingly involved, fewer arms are flowing across the Lebanese border.

"First of all, we need some international coalition of the willing," Ibrahim said. "If the U.S. openly starts arming, then the other countries will have more courage to start arming us, too. Otherwise, we will continue where we are: a situation where nobody is willing to act really and people continue to die while the radicals are gaining more and more ground."

Contributing: Jennifer Collins in Berlin; Dorell reported from McLean, Va., Kwider from Amman.