* Former Assad defence minister said to defect, reach Turkey
* Would be most senior of Assad's fellow Alawites to flee
* Putin criticises U.S. approach ahead of G20 summit
* Obama seeking congressional approval for strikes
* France says strikes do not prevent a political solution
By Khaled Yacoub Oweis and Amena Bakr
AMMAN/DOHA, Sept 4 (Reuters) - President Bashar al-Assad's former defence minister has fled Syria, opposition figures said on Wednesday, noting that General Ali Habib was the most senior of Assad's Alawite sect to defect.
Habib had been under house arrest since resigning in protest at Assad's crackdown on demonstrators in 2011 but had managed to reach the Turkish border late on Tuesday with Western help, Kamal al-Labwani of the Syrian National Coalition told Reuters.
Other sources also said Habib had fled but Syrian state television denied he had left his home and Turkey's foreign minister said he could not confirm the general had defected.
More verbal skirmishing on Wednesday between Moscow and Washington over U.S. plans to attack Damascus was tempered by talk of possible easing in the East-West deadlock when President Vladimir Putin hosts world leaders at a G20 summit on Thursday.
U.S. President Barack Obama said he would continue to try and persuade Putin of the need for punitive strikes on Assad for using chemical weapons when the two meet in St. Petersburg.
But Putin again questioned Western evidence. And he accused U.S. Secretary of State John Kerry outright of "lying" when, in urging Congress to approve strikes on Syria, Kerry played down the role of al Qaeda in the rebel forces. "Al Qaeda units are the main military echelon, and they know this," Putin said.
"He is lying and knows he is lying. It's sad."
Having surprised friends and foes alike by seeking approval from Congress before attacking, Obama has been building support ahead of votes in Washington expected next week. In Stockholm en route for Russia, he appealed to lawmakers' consciences:
"America and Congress's credibility is on the line," he said. "The question is how credible is Congress when it passes a treaty saying we have to forbid the use of chemical weapons."
Earlier, Putin had said in a pre-summit interview with the Associated Press that he could not absolutely "rule out" Russia supporting a U.N. Security Council resolution to punish Assad - if it could be proved he had used poison gas.
A senior Western official said that, while Moscow was unlikely to say so in public, there were signs Russian officials believe Assad was indeed responsible for the deaths on Aug. 21 and that it had strained Russian support for him - providing an opening for a new, concerted drive to end the conflict.
However, Putin's characteristically blunt tone towards the U.S. position appeared to limit prospects for a breakthrough in a stalemate that has prevented international action to rein in a conflict that has killed more than 100,000 Syrians and left millions homeless but which neither side has been able to win.
The rebels, largely drawn from Syria's Sunni Muslim majority, have captured large swathes of territory and won backing from Gulf Arab states like Saudi Arabia, as well as from Turkey and Western powers. But Assad, armed by Moscow and backed by Shi'ite Muslim Iran, has held on in Damascus and elsewhere.
Christians, Kurds and others, as well as Western leaders, are wary of Islamist militants among the rebels. Assad's fellow Alawites, an offshoot of Shi'ite Islam, fear annihilation if he loses and provide the backbone of the president's armed forces.
Numerous defections over the past two years by senior commanders, either to the rebel Free Syrian Army or into exile abroad, have not led to a collapse of Assad's defences.
But the flight of Habib, if confirmed, would lend credibility to suggestions that parts of the Alawite community may be turning against Assad. Previous high-level defections have generally involved Sunni officers.
"Ali Habib has managed to escape from the grip of the regime and he is now in Turkey, but this does not mean that he has joined the opposition. I was told this by a Western diplomatic official," the SNC's Kamal al-Labwani said from Paris.
A Gulf source told Reuters that Habib had crossed the Turkish frontier late on Tuesday with two or three other people. He was then taken across the border in a convoy of vehicles.
Born in 1939, Habib was defence minister from June 2009 to August 2011 and has also served as Chief of the General Staff of the Syrian Army. He is from the port city of Tartus.
Some opposition sources say that Habib disagreed with the use of force against protesters at the start of the revolt in 2011. Those sources say he was dismissed. He later said publicly that he had left the post for health reasons.
"Habib is a simple and honest. Unlike the Assads he is not corrupt," said a military defector who served under Habib.
"His defection will rattle the Alawite community because it will be seen as another man jumping off a sinking boat, indicating the coming fall of the regime."
Predictions of the imminent collapse of the four-decade-old Assad dynasty, including by Western leaders, have turned out to be wishful thinking before. Recently, the alleged use of poison gas has been cited as evidence of desperation in the Assad camp.
The head of German intelligence told members of parliament this week that German agents had recorded a call between the Iranian embassy in Damascus and a senior figure in Hezbollah, the Lebanese Shi'ite militia, which, the agents believe, betrayed a lack of confidence among these two key Assad allies.
A person who attended at the lawmakers' briefing on Monday said the material was presented as evidence of Assad's role in the release of poison gas in rebel-held suburbs of Damascus on Aug. 21. But it also indicated doubts about Assad's tactics.
The Hezbollah official said Assad's was wrong to order the gas attack and that it indicated he was losing his nerve. Germany has ruled out joining any military action in Syria.
Following the failure of British Prime Minister David Cameron to win parliamentary backing for air strikes last week, France is the only major military power lining up behind Obama. Its parliament debated Syria on Wednesday, though President Francois Hollande does not need approval for action.
His foreign minister, Laurent Fabius, said using force against Assad could pave the way for a new round of diplomacy.
French Prime Minister Jean-Marc Ayrault told parliament that failure to strike Assad would send a message to the likes of Iran and North Korea that they could defy Western powers with impunity, notably over concerns about their nuclear programmes.
Obama has won the backing of key figures in the U.S. Congress, including among his Republican opponents.
Leaders of the Senate Foreign Relations Committee said they reached an agreement on a draft authorisation for the use of military force in Syria. However, the draft is narrower than the request made by Obama and includes a provision barring the use of ground troops. Some senators have criticised the wording.
Among other provisions, the Senate Foreign Relations Committee draft, which was obtained by Reuters, sets a 60-day limit on U.S. military action in Syria, with a possibility of a single 30-day extension subject to conditions.
It requires Obama to consult with Congress and submit to the Senate and House of Representatives foreign relations panel a strategy for negotiating a political settlement to the conflict, including a review of all forms of assistance to the rebels. (Additional reporting by Laila Bassam, Yara Bayoumy and Erika Solomon in Beirut, Paul Taylor and John Irish in Paris, Alexandra Hudson in Berlin, Thomas Grove and Darya Korsunskaya in Moscow and Steve Holland and Matt Spetalnick in Stockholm; Writing by Alastair Macdonald; Editing by Giles Elgood)