By Dominic Evans
BEIRUT (Reuters) - Syrian President Bashar al-Assad has watched Arab uprisings bring down the leaders of Egypt and Tunisia in a few short weeks and topple Libya's Muammar Gaddafi, but shows no sign of yielding to protests challenging his own iron rule.
As street demonstrations against Assad reach the six-month mark this week, Syria has plunged deeper into bloodshed, economic stagnation and international isolation than most countries swept up in the turmoil of the "Arab Spring."
Any one of those crises could threaten the survival of the 46-year-old president, a member of Syria's minority Alawite sect who has ruled the mainly Sunni Muslim country since succeeding his late father Hafez al-Assad 11 years ago.
But Assad enjoys two crucial advantages over the deposed North African leaders, who were either cut adrift by their own security forces when the tide turned against them or forced to retreat by NATO bombs.
Syria's army has remained mostly loyal to the president, spearheading a relentless crackdown on protesters in which the United Nations says 2,600 people have been killed.
And while the repression has triggered Western sanctions and regional criticism, Assad knows there is little appetite for military intervention in a country with more regional allies than Libya and a potentially volatile ethnic and religious mix.
"There is clearly no incentive for the international community to step in as in Libya," said Alan Fraser, Middle East analyst at the London-based consultancy AKE.
"The sad truth is that at present the chaos has minimally affected anywhere outside its borders. There are no major economic resource issues affected, while the politics of the country is so complicated that no one wants to meddle."
Protests in Syria, one of the most tightly controlled Arab states, first broke out on March 16 when police broke up a silent demonstration of 150 people, mainly women, in the capital Damascus, seeking the release of political prisoners.
Two days later security forces shot dead three protesters in the southern city of Deraa. Demonstrations spread across the country and in April Assad sent the army into Deraa, the first of many military assaults aimed at crushing dissent by force.
Although the crackdown has failed to end the protests -- activists say there are sometimes more than 100 demonstrations in a single day -- they are smaller than the peak in July when at least 100,000 people gathered on Fridays in the city of Hama.
Activists have reported a steady but modest flow of army desertions, mainly low-level Sunni Muslim conscripts.
Some have clashed with security forces and others have formally announced their defection, but as yet they have no territory of their own from which they could challenge the army.
Apart from Assad's replacement of his defense minister last month -- a move attributed to ill health -- there has been no sign of upheaval in senior military ranks, dominated by members of his Alawite minority.
"If the army can maintain its cohesion, there's very little you can see that would change the balance of power," said Julien Barnes-Dacey, Middle East analyst at Control Risks.
But exploiting that overwhelming military superiority over a mostly peaceful protest movement has come at a cost.
Assad's repression of the unrest has led to Western sanctions and calls for him to step down, as well as growing criticism from Arab and regional countries.
"The Syrian people do not believe in Assad. Nor do I," Turkish Prime Minister Tayyip Erdogan, a former ally of the Syrian leader, told Arab foreign ministers in Cairo on Tuesday.
At the same meeting, Arab ministers called for "immediate change...to halt the bloodshed" in Syria.
The United States and European Union have agreed a range of sanctions including an embargo on Syrian oil exports which, coming on top of a collapse in tourism revenues and sharp fall in trade, mean Syria faces gradual economic meltdown.
However Assad has weathered international crises and isolation before, particularly after the 2005 assassination of Lebanese statesman Rafik al-Hariri when an initial U.N. investigation pointed to Syrian involvement.
"The nature of Syria's isolation over the last decade is that they are well accustomed to being out on their own. They don't have these political and economic ties which make them dependent on outside players," Barnes-Dacey said.
By imposing sanctions and calling for Assad to go, Western powers have already pulled the few levers of influence they have over Syria, and have yet to convince China and Russia to back a tough United Nations resolution against Damascus.
Equally divided are Syria's opposition figures, who have failed to unite around an agreed platform, bridge gaps between those inside and outside the country, or coordinate fully with grassroots protesters who continue their defiant demonstrations.
Assad has promised reform including a multi-party election next year, but has not said whether he will allow a presidential challenger when his term expires in 2014. Opposition figures say the continued violence undermines any pledges of change.
Syria's Baath Party leadership needs only look next door to neighbouring Iraq to see another Baathist ruler, Saddam Hussein, who survived more than a decade of war and sanctions.
Assad's father, Hafez al-Assad, also survived popular unrest, killing many thousands of people when he crushed an armed Islamist uprising in the city of Hama in 1982.
One Damascus-based diplomat said Bashar still retains solid support among the bulk of his minority Alawite community, some Christians who fear post-Assad Sunni Muslim majority rule, and sections of business class of Aleppo and Damascus.
But if the protests and repression continue, his position and support would steadily weaken in the long term, eroded by economic woes and ever-growing resentment.
He could also face an increasingly armed uprising.
Rights groups say street protests have been overwhelmingly peaceful so far, but there have been reports of attacks on security forces. Syrian authorities say 700 soldiers and police have been killed.
In the absence of a strong, unified opposition, the diplomat said the biggest potential threats to Assad would come from an internal coup, a big wave of military defections, economic collapse or one of the two main cities -- Damascus or Aleppo -- siding with the protesters.
None of those appeared imminent, he said.
"Assad will never exert the control over Syria that he once did. The unrest is too widespread for a Hama-style crackdown" said Fraser. "However it is going to take a lot to topple him.."
(Additional reporting by Peter Apps in London; Editing by Jon Boyle)