By Alexander Dziadosz

TRIPOLI, Lebanon (Reuters) - For two weeks now, the rifles have been silent along Syria Street in Lebanon's Tripoli, an area shot up so often that even memorial posters of men killed just a few months ago are speckled with bullet holes.

Soldiers patrol quiet streets where gunmen used to fight day and night - part of the Lebanese authorities' most serious effort yet to contain spillover from Syria's civil war since the three-year-old conflict began in its much larger neighbor.

But while many in Tripoli, 30 km (20 miles) south of the Syrian border, have welcomed what they see as an overdue clampdown, they also worry it could falter under renewed political bickering and a backlash by radical Sunni militants.

"Traffic is returning, the area is coming back to life," said Ahmed Qashour, 57, raising his voice as armored vehicles rumbled past the tahini sesame-paste shop where he works on Syria Street, in the north of the Mediterranean port city.

"But what we want, what we're asking of the government, is that this security plan continues - that it doesn't stop."

Syria's civil war has divided Lebanon's politicians, while gunbattles, car bombs and rocket attacks linked to Syria have killed scores of Lebanese and revived memories of the country's own 15-year civil war that formally ended in 1990.

Disputes have been particularly acute over the Shi'ite movement Hezbollah's move to send fighters to aid Syrian President Bashar al-Assad, a fellow ally of Shi'ite Iran. Some Lebanese Sunnis have meanwhile joined the rebels.

The fact that the clampdown is happening now indicates a rare moment of agreement among international, regional and domestic players who all have an influence on Lebanese politics, analysts and officials say - although there is still plenty of scope for things to go wrong.

"There is an intersection of interests between all parties to have Lebanon stable these days," said Elias Hanna, a retired Lebanese army general and senior lecturer on geopolitics and war studies at the American University of Beirut.

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"You cannot really afford to have Syria, Iraq and Lebanon - this axis of instability - going into havoc."

DIVIDED BY SYRIA STREET

Tripoli is a microcosm of the ruptures that have made Syria's war so toxic and symbolic of how the conflict has rejuvenated decades-old rivalries in Lebanon.

Like Syria, Lebanon's second city is mostly Sunni with a minority of Alawites, the Shi'ite-derived sect to which Assad and much of his security establishment belong.

Tensions between the two communities have erupted most spectacularly in gangland-style fighting between two districts on the northern edge of town that are divided by the appropriately named Syria Street where Qashour works.

Residents from both neighborhoods have fought off and on since Lebanon's civil war ended 24 years ago, but Syria's conflict has pushed the violence to new levels.

Until recently, the authorities have been unable or unwilling to stop the fighting, residents say, chalking up the failure of previous crackdowns to disputes between politicians who stood to gain more than they lost from the conflict.

"Politicians were in disagreement, and so when the security plan would come down, the army would arrive," Qashour said. "The journalists would come and take pictures of them, and then after two or three hours you wouldn't see anyone."

But, like other residents, he said he detected a new seriousness in the latest effort, which started last week after around 30 people including an army officer and a 10-year-old girl died in the latest round of fighting.

"This is the first time I've been able to relax," said Fouad Fahed, a merchant at the local market.

"Apparently there's political cover for the army now."

RADICAL BACKLASH

One of the biggest risks of the campaign is the threat of a backlash from hardline Lebanese and Syrian Sunnis who see double standards in a crackdown on Sunni militants while Hezbollah maintains a militia that rivals the Lebanese army in strength.

Already, there are signs some Sunni militants are turning to attacks against the army: car bombs and shootings have killed several soldiers over the past month - common enough in Iraq and Syria but rare in Lebanon, where the religiously mixed army is often portrayed as a pillar of national unity and stability.

On Tuesday, a hardline Sunni cleric, Dai al-Islam al-Shahal, denounced the army raids on live television, warning against the military becoming "a rod in the hands of Hezbollah and Iran".

"I say with all honesty and clarity, that Lebanon is being held captive," he said, his voice rising in anger.

"Let's not be in denial, Lebanon is captive. Some want our army to be pushed into following the example of the Syrian army, killing its own people and being led by shabbiha," he added, referring to irregular fighters in Syria who support Assad.

While few Lebanese Sunnis are likely to put it so caustically, Shahal is not the only one to voice bitterness.

A group calling itself the Lebanese branch of the Nusra Front, al Qaeda's Syrian affiliate, has branded the army a legitimate target because of its perceived help for Hezbollah.

Firebrand cleric Ahmed al-Assir, whose supporters fought a gunbattle with the army in June, has called for Sunni soldiers to desert - a nightmare scenario which, however unlikely, recalls Christian-Muslim fractures during the civil war.

POLITICAL COVER

Supporters of both Hezbollah and their political rivals in the Sunni-led Future Movement each frame the concord on deploying the army in Tripoli and in other troubled areas near the border as evidence the other has seen the error of its ways.

"For three years, we in the Future Movement have been asking for the deployment of the army in Tripoli and disarmament in the city," said Ahmed Fatfat, a Sunni lawmaker from north Lebanon.

"But despite there being a security plan, unfortunately there was no political cover."

Hezbollah, he said, had now shifted its stance partly because of fallout from its Syria intervention, which analysts say has killed hundreds of its fighters and provoked retaliatory attacks by Sunni militants against Shi'ite areas in Lebanon.

A senior figure in the Hezbollah-led March 8 coalition gave a mirror-image interpretation, saying the breakthrough came because leaders in Future's March 14 coalition has realized the threat from radical Sunni militants was too great to ignore.

Hanna, the retired general, pointed to advances by the Syrian army and its Hezbollah allies in areas of Syria along the Lebanese border over the last month as another factor.

Now much of the Syrian side of the border was firmly held by the Syrian army, Hezbollah was, he said, less concerned about a deployment of Lebanese troops hindering its fighters' access to Syria: "It is a win-win for Hezbollah," he said. "And it is a must for the Sunnis and the Future Movement."

"BODY WITHOUT A HEAD"

Despite discontent among hardliners, support for the army runs strong among Sunnis, including in the hillside villages of Akkar, a northern region of green valleys and terraced farms where two soldiers were gunned down on Tuesday.

While the terrain and proximity to Syria pose risks for anyone trying to police the region, residents insist the killing of the two soldiers was an isolated incident and that soldiers should consider themselves safe from attack by locals. "The army is a red line for us," Ali Ismail, a local resident, said.

People in the area have economic as well as patriotic motives for their support - the army offers one of the few chances of stable jobs in the poor, largely agricultural region, meaning many have husbands, sons and brothers in the military.

"Here in Akkar, we depend on the state and the army for employment," said Hussein Ammareddeen, 26.

"The army are the ones who protect us. Who else would protect us?" he added, saying that Sunnis only had individual arms to protect themselves rather than an organized force.

All of this makes it unlikely Sunnis would turn against the army en masse - but it also does little to assuage widespread resentment of Hezbollah's dominance and a sense that the Shi'ite movement has consistently outmaneuvered Sunni leaders.

Sectarian allegiance matters in a nation of some 4 million which French colonial rulers carved out from Syria and whose political institutions are intended to balance power among its Christian sects, Sunnis, Shi'ites and other religious groups.

Despite the inclusion of Sunnis in a new coalition cabinet - including the interior minister - the bloc's leading figure, former prime minister Saad al-Hariri, fled abroad in 2011.

That leaves many fellow Lebanese Sunnis anxiously feeling they lack strong leadership to defend them as sectarian rancor fuelled by Syria's war spreads across the Middle East.

"As Sunnis in Lebanon, we are a strong body, but a body without a head," said Bilal al-Masri, a prominent figure in Tripoli's fundamentalist Salafi movement. "There's no good in a body without a head, and no good in a head without a body."

(Editing by Alastair Macdonald)