* Once-loyal city stunned by fierce fighting
* Assad seen alienating Syria's commercial hub
* Refugees from Aleppo flee battle zones
By Suleiman Al-Khalidi
ANTAKYA, Turkey, Aug 3 (Reuters) - Syrians fleeing fighting in Aleppo are furious that President Bashar al-Assad could turn so much firepower on a city that had stayed mostly aloof from the 17-month-old revolt against him.
Some say Syrian leader's decision to unleash warplanes, helicopter gunships, tanks and artillery against rebels seeking to seize Aleppo could prove fatal to his chances of survival.
"I never expected Assad to do this," said Nabil Najjar, a 72-year-old carpenter, sitting on a mattress in a sparsely furnished two-room flat in the Turkish city of Antakya.
"Aleppo is his downfall," he said. "His father (President Hafez al-Assad) warned him: 'if you want to stay in power, win Aleppo'. He has lost it and now his throne is crumbling."
For Najjar, the street battles revive memories of a military campaign by Assad's father 30 years ago to crush an armed Muslim Brotherhood uprising in Hama and Aleppo. Many thousands were killed and the entire old quarter of Hama was razed.
The younger Assad may now have alienated many hearts and minds among Aleppo's 2.5 million people, but the 10-day-old military struggle for Syria's biggest city seems far from over.
"The focus is now on Aleppo, where there has been a considerable build-up of military means, and where we have reason to believe that the main battle is about to start," U.N. peacekeeping chief Herve Ladsous said in New York on Thursday.
The Syrian refugees lodging in cheap apartments in Antakya's Haci Omer district alongside Turkish neighbours of Arab descent will find it hard to believe the war that has suddenly engulfed their ancient trading city could get any worse.
Musa Hariri, a tailor, fled to Turkey on Wednesday hours after he buried his six-year-old daughter Sama, killed by Syrian army shelling of their home in Aleppo's Salaheddine quarter.
"We buried Sama, God rest her soul in peace, and rushed here. At least here there is no Assad army, no shelling, no sounds except those of people," said the distraught 42-year-old.
Abdul Rahman Sabbagh, 34, a welder, said he had left with his wife and five children to escape gunfire and explosions.
"For days we heard nothing except the sounds of bullets and the indiscriminate shelling," he said. "Every 30 seconds there would be a missile. We could not bear the shelling."
Along with the anger is a sense of disbelief at the punishment meted out to Aleppo, Syria's economic powerhouse, and long perceived as a bastion of loyalty to Assad's rule.
Some refugees recalled how Assad spent two weeks in Aleppo before the revolt began in March 2011, dealing with local discontent. He sacked the city council, hated for its corruption, and promised to meet demands for better services.
When anti-Assad demonstrations erupted around the country, Aleppo stayed quiet, its wealthy Sunni Muslim merchant families still more comfortable with an Alawite-dominated system that had allowed them to prosper than with the uncertainties of change.
Support for Assad as a guarantor of stability remained strong among Aleppo's Sunnis and its Christian minority even when troops and security agents sought to quell pro-democracy demonstrations in provincial cities like Deraa, Hama and Homs.
The authorities recruited thousands of pro-Assad shabbiha militiamen in Aleppo to counter protests and crush dissent.
WATCHING FROM SIDELINES
Months later, when Assad's opponents began taking up arms and the military started shelling rebellious cities, many in Aleppo remained sceptical about reports of the repression.
"We in Aleppo did not believe it ... until we saw this with own eyes," said Omar Jaleel, a 50-year-old plumber still in shock at the ferocious bombardments he had just survived.
"Everyone is now against Assad," he said in Antakya.
While Aleppo had stayed on the sidelines of the uprising against four decades of Assad family rule, tension had been rising and scattered opposition protests met a stern response.
Security forces have shot dead dozens of demonstrators in Aleppo this year, fraying the de facto alliance between the city's Sunni business class and Assad's ruling system, based on his minority Alawite sect, a distant offshoot of Shi'ite Islam.
But it was fighters from the countryside who plunged Aleppo into the conflict when they tried to seize the city on July 24, emboldened by a rebel offensive in Damascus that followed a bomb attack on July 17 in which four senior Assad aides were killed.
Once-bustling commercial districts are now battle zones, where rebels take cover in deserted buildings or man checkpoints amidst a few terrified residents who have stayed behind.
"In my street, there are 10 buildings and there is not a single person left. They all fled, some to farms, some to other villages or to Turkey," said one refugee in Antakya, Osama al-Ashqar, holding his four-year-old boy Omar in his lap.
"Everyone went with his instinct. When you see the fear in the eyes of your children, you only have one thought and that is to leave," said Ashqar, estimating that more than 300 families in the central Bustan al-Qasr neighbourhood fled in 24 hours when assaults by helicopter gunships intensified.
They would pack up and go during daylight lulls in shelling, leaving everything except cash and jewelry, refugees said.
Omar Billal, a biscuit factory worker, left his Saif al-Dawla neighbourhood at dawn when overnight shelling eased.
"At night you cannot open a window and look at the street because army snipers are everywhere," he said.