AMMAN (Reuters) - The commander of Syria's main rebel force is coming under increasing pressure to impose unity on his fighters as the United States and other powers move towards arming the opposition battling to overthrow President Bashar al-Assad.
General Salim Idriss, a defector chosen six months ago as consensus figure to lead the rebel Supreme Military Council, is being promoted as a cool head to bring together fractious combat units and curb the influence of radical Islamists.
Idriss's Supreme Military Council, which runs the Free Syrian Army that looked on the verge of toppling Assad last year, is trying to recover from the loss of the town of Qusair to government troops reinforced by the Iranian-backed Hezbollah militia this month.
Washington's decision to arm the council, an umbrella group organised into five geographical fronts, and reports that weapons are also coming in from the Gulf, have put the onus on the East German educated former military academic to forge a single rebel front.
His response to Washington's offer of military assistance was to call for heavy weapons to fight off an assault on the northern city of Aleppo by Assad's forces, a battle he must win to keep his campaign on track.
In the absence of a unified political opposition, Idriss is also assuming a political role by sending delegates to the Syrian National Coalition, the civilian arm of the opposition.
But first Idriss has to impose discipline on his own officers and improve the reputation of the military council, which have proved less effective than hardline Islamist units and has struggled to assert its authority on the battlefield.
Like Idriss, most defectors in the Military Council are Sunni Muslims, a group who form the majority of Syria's population and most of the opposition to Assad.
Sunnis also formed the bulk of the army but had little influence in an organisation dominated by members of Assad's minority Alawite sect, an offshoot of Shi'ite Islam that has controlled the military and security apparatus since the 1960s.
Away from the battlefield, the military council has had disagreements over strategy, but Idriss has shown skill in defusing them, notably over a proposal by one commander who wanted to hit Hezbollah in Lebanon after the Qusair defeat.
Although Idriss agreed with the officer, colonel Abdeljabbar al-Oqaidi, that Hezbollah is propping up Assad and is seeking to expand its gains in central Syria, Idriss opposed expanding a war to topple the Syrian leader into Lebanon, the sources said.
This pragmatic streak has won Idriss backers in the West and among members of the political opposition, who hope he may help bring together a divided opposition which has failed to elect a leadership or form a planned provisional government.
One opposition official said Idriss proved himself two months ago at a meeting of the pro-opposition Friends of Syria grouping in Istanbul which almost collapsed when the Syrian delegation head, Moaz al-Alkhatib, walked out to protest international inertia in the face of what he said was the slaughter of Syrian civilians.
"Alkhatib literally threw a fit and walked out. Idriss took over and saved the meeting. The Turks who were sceptical of him realised how much they owe him," the official said.
But impressing international powers is one thing. Convincing sceptical Syrian rebels - who see Idriss as more of a spokesman and arms procurer than genuine leader - is a tougher challenge, and increasingly urgent as Assad's forces win back rebel ground.
"Idriss has done well as an interlocutor with the West and the Gulf, but the military situation is degenerating ... It is not too late to save it but he does not have much time," said a senior opposition figure who did not want to be named.
"The Islamists do not like Idriss but they do not hate him either," the source said.
Islam Alloush of the Liwa al-Islam brigade, one of the strongest Islamist rebel units, said his group is willing to cooperate with Idriss and is in touch with the Military Council.
"We consider any one who is fighting to rid Syria of Bashar al-Assad to be with us," Alloush said.
Strengthening the Military Council with arms would help the moderates carve a bigger role in the military struggle against Assad and redress the balance of power with Islamist rebel units, especially in eastern Syria, where Salafist groups such as Ahrar al-Sham and al-Qaeda linked Nusra Front almost singlehandedly captured the city or Raqqa.
Diplomats say the rationale behind the Western support for Idriss is to create a well-financed and well-armed formation that would attract fighters who until now had little option but to join more radical Islamist units.
"Western officials have flatly told us they do not want another Rwanda in Syria where the Alawites would end up annihilated. They want to strengthen the opposition enough to force Assad to concede a political transition and leave the country," an opposition leader said. "Idriss's core strength is that he is rational. He fits the bill."
Idriss told Reuters his main aim was to see Assad leave power to build a "tolerant, democratic Syria."
Militarily the main challenge is to obtain enough weapons to strengthen all five fronts and counter fighters from Hezbollah, Iran and Iraq, of which he said about 15,000 were in Syria, giving a major boost to the 50,000 troops Assad can rely on.
A shipment of Konkurs anti-tank missiles to military council units in Aleppo last week has already helped stem the advance of Assad's forces who had exploited a gap in rebel lines northwest of Aleppo.
"We do not belittle the military ability of these fighters, especially from Hezbollah, who are well-trained and are being led by Iranian officers and use a different technique," Idriss said. "We've absorbed the shock. We are starting react and counter them."
Editing by Giles Elgood