By Laila Bassam

TRIPOLI, Lebanon (Reuters) - The battle-scarred streets of this hilltop enclave have fallen quiet, but fighters say the shaky truce is a mere pause in a conflict that has just begun and which threatens all Lebanon.

Jabal Mohsen, a minority Alawite district of the northern port city of Tripoli, has for decades been at the ready for sporadic clashes with the impoverished, majority Sunni Muslim Bab al-Tabbaneh neighborhood that sprawls beneath it.

The latest violence, the heaviest in years, broke out about 10 days ago. It has been triggered by Syria's civil war, which has stoked sectarian violence between Sunni Muslims, who lead the revolt against President Bashar al-Assad, and Assad's minority Alawite sect, an offshoot of Shi'ism.

Those faultlines are reflected in the on-off battles that have erupted over the past two years in Tripoli.

But this time, local Alawite leader Refaat Eid says, the fighting which took 29 lives last week stands ready to spread throughout Lebanon as tensions inspired by Syria's two-year conflict continue to rise.

"I'm not optimistic, (although) there is a ceasefire now. Whoever wants to cut their hair can cut their hair, whoever wants to bathe can bathe," said the tall, bulky man with a shaven head.

"And for those who used up their ammunition, they can get more and wait for the next battle."

Clashes broke out between Tripoli's opposing communities again after the beginning of a critical battle now raging over the Syrian border town of Qusair between rebels and Syrian government forces backed by Shi'ite Hezbollah fighters.

Qusair, a town of 30,000, has been a smuggling transit point for Syrian rebel weapons and fighters. Many believe Tripoli was part of the cross-border supply route now under threat.

Control of Qusair would help Assad cement a route between the Syrian capital Damascus, and his Alawite stronghold on the Syrian Mediterranean coast, north of Lebanon's Tripoli.

Syria's conflict has exposed the divisions that still run deep through Lebanon. As Hezbollah fights with Assad in nearby Qusair, former Sunni Prime Minister Saad al-Hariri has been backing the opposition. Sunni fighters from northern Lebanon and east have also joined their Sunni brethren in Syria.

Eid says the importance of the battle for Qusair made clashes in Tripoli inevitable.

Lebanon's entire political spectrum has called for calm in the city, from the former Sunni Prime Minister Najib Mikati to Shi'ite Hezbollah leader Hassan Nasrallah.

"There is no solution, because the state no longer has any weight," Eid said.

"EXISTENTIAL STRUGGLE"

The recent round of clashes in Tripoli which ended over the weekend was the heaviest in years. Fighters used 107 millimeter rockets, machineguns, and rocket-propelled grenades.

Syrian flags fly over buildings pocked with bullet holes in the Alawite district of Jabal Mohsen - traces of fighting going back 40 years.

Along the district's main road, shattered car windows have been replaced with nylon rather than glass. "We put nylon in our car windows just like we did with the windows at home, because we will definitely see another battle, and every time all our windows break," a resident said.

"Why trouble ourselves fixing things every time?"

At the entrance to Jabal Mohsen, riddled with holes from sniper fire, a large banner of Assad has been hung, reading "Our eternal leader", and posters of the young men killed in fighting here.

There are also pictures of Assad's father, Hafez, who ruled Syria for nearly 30 years, and sent Syrian troops in to Lebanon. Syria maintained a military presence in Lebanon until 2005.

During Lebanon's 1975-1990 civil war, Alawites in Jabal Mohsen supported Assad's forces against Sunni fighters in Bab al-Tabbaneh district who were supporting Palestinian militants.

Years of long, bitter tensions make Alawite fighters feel that with each round of clashes, the stakes are rising.

"We consider this an existential fight. Our struggle is for survival," Eid said.

He holds up an empty red canister fired at Jabal Mohsen from below. He points to a short inscription printed on its side: "This was produced by the blood of the martyrs. It is not permitted for resale. The Free Syrian Army."

Alawite fighters here say they see this as a proof that they are no longer fighting just the Sunni men of Tabbaneh, but also Syrian rebels they believe are taking shelter in Tripoli.

"No one can blame us, because we have no guarantees," Eid said. "Our only guarantee is our own strength."

The gunmen in Jabal Mohsen justify their rising militancy by pointing to the Lebanese army's failure to prevent the clashes here. Soldiers occasionally roam the street in tanks, but have been unable to stamp out the fighting.

"In the beginning we had protection, the Lebanese army. But now, it has lost four martyrs of its own and had 86 others wounded in the last battle," says Abu Ali al-Zamar, a combat unit leader in his late 20s.

In his dark sunglasses and tight Armani T-shirt, he surveys his men's positions on the hill.

"The army cannot defend itself. So how can I expect to defend me? I consider this truce to be a break. But my hand is on the trigger, and I'm waiting."

(Editing by Pravin Char)