By John Irish
PARIS (Reuters) - It's a warm day on the Turkish-Syrian border. France's recently recalled ambassador to Syria is incognito with his deputy and a security agent.
After checking the surroundings are clear, the diplomat pulls out a stash of brown envelopes stuffed with thousands of dollars. The recipients are "viable" rebels operating in zones no longer under President Bashar al-Assad's control.
The scene last September, recounted by French officials, could have come from a spy film. Now Assad's forces appear to be regaining the upper hand on the battlefield.
The change in the balance of power is causing alarm in Western and Arab capitals. Having clamored for Assad to step aside, none of his foes have been ready to take the risk of providing anti-aircraft or anti-tank weapons that could tilt the balance.
President Barack Obama authorized sending U.S. weapons to the rebels for the first time, a U.S. official said on Thursday after the White House said it has proof the Syrian government has used chemical weapons against opposition forces. However, it remains unclear what kind of weapons will be sent.
With the opposition fragmented, the West has long feared that weapons could fall into the wrong hands, notably al Qaeda-backed militants and the Islamist Nusra Front, and has wanted "guarantees" from opposition fighters before providing the arms.
With cast iron guarantees unlikely and time running out, the way France has developed its networks in Syria since the uprising started more than two years ago offers an idea of how Western powers may assess future military help.
"It's not possible to say that we can be 100 percent sure about where the weapons go," said a Western diplomat. "But the risks of porosity are less than the risks of doing nothing."
France's active support of rebels in its former colony stems in part from a wish to secure trade interests. It fears that the window to unite the opposition is disappearing and the longer disunity prevails, the more likely Islamist and al Qaeda elements, hostile to the West and now among the insurgents fighting Assad, will emerge on top.
France and Britain can now technically arm rebels after they pushed to have an EU arms embargo lifted. Saudi Arabia, Qatar and Turkey already supply light weapons.
Almost from the onset of the uprising Paris tried to develop internal networks and gain trust among opposition activists. Before recalling its ambassador from Damascus in March 2012, the embassy had been smuggling medicines clandestinely to makeshift hospitals and food for protesters.
Six months later, Foreign Minister Laurent Fabius announced a plan to aid "free zones" in northern Syria.
The objective was primarily to reach local communities no longer under Assad's control and help them revive local administration and restore basic needs, such as bakeries.
Paris insisted on a strict system of traceability for how its cash was spent. For every dollar, receipts and as much photographic and video evidence as possible had to be provided. It also relied on informers who reported back.
Most of the "revolutionary councils" had civilian and military branches. The military wings were the embryo of the Free Syrian Army. It enabled Paris to begin mapping fighters.
"It wasn't technical advice. It was first and foremost to develop links between the political opposition, defectors and rebel fighters so they could speak to each other and agree to work together," recalls one French official.
The subject of providing artillery to protect these zones was under already discussion, although the implications were deemed too complicated. Paris felt that until a legitimate opposition government was in place it would not be possible to give military support.
That was in part why President Francois Hollande was first to recognize the Syrian National Coalition in November. The coalition would have a military wing that Paris could deal with.
Gone were the brown envelopes. Almost immediately France diverted its bilateral help to the coalition's Aid Coordination Unit run by vice-president Suheir Atassi.
In parallel to this, France also channeled medical and humanitarian aid in large part through the Union of Syrian Medical Relief Organisations (UOSSM), a non-governmental association based in Paris that brings together 14 groups.
France is its largest donor. Medical convoys - the latest a 20-tonne cargo due to arrive in Turkey in the next few weeks - are sent to a hospital partly built with French cash just across the Turkish border.
From there the goods are distributed across Syria including to some of the areas where there has been fierce fighting, mostly recently to the Qusair region where Assad's troops and Hezbollah fighters defeated rebel forces.
While the UOSSM maintains it takes no sides, Paris has some say where the aid is dispatched. It enables it to form a detailed analysis of developments on the ground.
"Our biggest challenge is that other countries just don't want to give money to an NGO that isn't known," UOSSM official Obaida al-Moufti said. "The French are very official. We present our project, document it and even though it's medicines they demand draconian traceability conditions."
HOW VIABLE IS FREE SYRIAN ARMY?
The French insist that these humanitarian, medical and civilian networks have been tested and provide a "cartography" of where future help could go.
"One needs to have precise knowledge of these fragmented groups," said a French diplomat. "We have a slight advantage because for a long time we've had direct contacts in the liberated zones and have already delivered material."
Their primary interlocutor for the last six months has been the head of the Free Syrian Army, Salim Idriss, whom French officials hold in high regard. Non-lethal aid ranging from bullet proof vests, night vision goggles or communications equipment has gone through him.
But his credibility is under question. Without money, munitions and weapons, he is struggling to assert his authority on the disparate groups of fighters, some of whom have said he is rather like a "schoolteacher".
Resolving that, officials say, will need two things. First, countries that supply weapons to rebels must coordinate better and ensure they work solely through Idriss.
Secondly, Western nations that remain cautious in providing weapons must widen the scale of their help, either in terms of equipment or "technical assistance" such as through battle tactics or weapons training.
"We've tested a certain number of these FSA elements," French foreign ministry spokesman Philippe Lalliot said. "We've built up trust and it's the similar types of assurances that we would like for weapons."
Ultimately the easiest way to ensure weapons do not fall into the wrong hands would be to find ways to track them. Fabius said last month that Paris was studying ways to monitor and neutralize weapons under certain conditions.
According to one official, options would include programming a time period for their use, limiting ammunition, placing global positioning systems on them or even turning them off from afar.
"I imagine that would only happen with more sophisticated weapons such as shoulder-fired MANPADs (man-portable air defense systems)," said Jeremy Binnie, Middle East and Africa editor for IHS Jane's Defence Weekly.
"It is technically possible you could get something in there to disarm them, but how much cost and the time it's going to take I think may be more of the issue."
(Reporting by John Irish; Editing by Giles Elgood and David Stamp)