(Reuters) - Sheikh Abu Abdullah Zahed, a Lebanese Muslim cleric with influence amongst radical youth, is part of a growing effort to push the uprising in Syria towards militant Islam.

Hardline Sunni Muslims in Lebanon are maneuvering for influence over Syrians across the border who have spent the last year fighting to topple President Bashar al-Assad.

"At first Syrians called on the West and NATO. Now they are calling on God," said Zahed, sitting in his library, where black Islamic flags hang on the walls.

As opposition groups abroad squabble over politics and Assad´s army pounds rebellious cities, Muslim hardliners want to make religion the unifying basis of the revolt.

Radical Islamist elements are still on the fringe, but that´s enough to make a headache for opposition activists who are struggling to convince Syrian minorities to support a revolt led mostly by the country´s Sunni majority.

Foreign powers joining exile opposition leaders at a "Friends of Syria" meeting in Istanbul this week will also want proof of whom exactly they are making friends with, if they are ever to consider arming rebel forces.

"We don´t want to accidentally wind up supporting extremist groups," said Joseph Holliday, of the Institute for the Study of War, in Washington. "The fundamental question is: What happens in the future? And does our involvement make this turn better or worse?"

Some activists are already uneasy about a series of car bombs that hit Syria´s two main cities. An unknown group called Al-Nusra Front claimed the attacks on a website that posts messages from many al Qaeda branches.

"There is a growing radical presence inside Syria and I think they were behind the bombings. I´m afraid controlling them could be a losing battle," said an activist. He asked not to be named for fear of angering fellow opposition members, who are reluctant to discuss potential radical infiltration.

STEREOTYPED BY BEARDS

Zahed, a Lebanese sheikh with a long beard and a leather jacket over his blue robe, sits in front of shelves of gold embossed religious books. He offers the Islamic flags that hang behind him to people who join anti-Assad protests in his hometown of Tripoli.

"At first no one raised anything other than the Syrian flag. Now some are raising the Islamic flag," Zahed said.

Assad has long raised the specter of Islamic extremism and says "terrorists" are behind Syria´s bloody uprising.

Activists say they lead a grassroots, inclusive movement but are unfairly stereotyped because many of them are religious.

"I want a pluralistic state that is democratic and belongs to everyone. Why are people so afraid? Yes, our revolution has Salafists, we have Islamists. Everyone is participating in the revolution," said a Syrian activist in Tripoli who calls himself al- Shami, which means "the Syrian".

He tugs on his brown, bushy beard: "Do we have to shave our beards so people don´t feel threatened? We´re not terrorists."

It is hard to know what impact radical groups are having in Syria, which has restricted access to journalists. But here in Lebanon there are signs they are gaining ground.

From the seaside city of Tripoli to border towns along the rocky foothills of Syria where rebels and refugees cross the frontier, Salafists are showing up in greater numbers.

When night falls on the border, dancing Syrian protesters set tires ablaze and fly their colorful independence flag. But as the flames grow higher and the night wears on, they are overtaken by young men whose black banners emblazoned in white Arabic script declare: "There is no God but God."

Members of this hardline, austere brand of Islam say they are drawn to the revolt because their religion says they should aid the oppressed.

But some clearly resent Syria´s minority Alawites, an offshoot of Shi´ite Islam, to which much of Syria´s powerful elite belong, including the president. Many Sunnis feel the government discriminates against them in favor of Alawites.

Some Syrian activists sheltering in Lebanon say Salafist clerics don´t represent them but are taking over at rallies.

"I try to speak at protests and some sheikh comes up and takes over. These protests are for the people not the sheikhs. Then we are all accused of being Salafists and sectarians," shouts Musaab in Wadi Khaled, a farming village on the mountainous border with Syria.

Salafists say they are gaining followers because they offer food and money to refugees as well as supplying many doctors and clinics that treat wounded Syrians smuggled into Lebanon.

"The state has fallen short in terms of helping the Syrians but we are happy for it. People who come here for help will leave with more Islamic thinking," said the cleric Zahed.

"CALL US TO JIHAD"

Some Islamists are struggling to prove that their conservative views do not make them militants who can´t work with foreign powers.

The Syrian Muslim Brotherhood, the largest and most organized opposition group abroad, includes followers from many Islamic backgrounds. It is in Turkey this week meeting with foreign powers along with secular and minority leaders.

The group has set out a platform for a future Syria that is democratic and pluralistic. But it has yet to convince minority groups who are wary of the balance of power and fear Islamists will change their tone if the uprising succeeds.

But activists in Syria say it is that radicals next door that have some activists worried. They point to calls for jihad, or holy war, by some protesters.

"If the Syrians call us to jihad we will do it, God willing. The UN can call it international terrorism or whatever they want," said Sheikh Salem al-Rifai at his Tripoli mosque, as crowds of men filed out from afternoon prayers.

Minor Syrian clerics have already called jihad but many Syrian sheikhs are wary and appear to be holding off an irrevocable escalation that would allow in foreign fighters.

There are already reports of Iraqi, Libyan and Lebanese fighters entering Syria and activists say they may be motivated by Sunni sectarian loyalties.

Many Lebanese and Syrian Sunnis harbor deep resentment against Alawites and the Assad government for bloody crackdowns in both countries, particularly the late president Hafez al-Assad´s crushing of a 1982 Islamist revolt in Hama. His forces razed parts of the city and killed more than 10,000.

One man´s view that is eagerly awaited is exiled Adnan Arour, an influential cleric who has said Alawites loyal to Assad should be "ground into dog meat".

Last month he hinted he was close to "ringing the bell" of jihad but wanted to see more solidarity among the rebels first.

RACE FOR ARMS

In the meantime, groups such as al Qaeda could appeal to poorly armed rebels facing tanks and artillery.

Zahed, the Lebanese sheikh, said al Qaeda sympathizers were certainly interested in Syria but he had seen no evidence that the militant network was setting up a base in Lebanon or Syria.

"Al Qaeda would need more time. It´s like opening a new branch of a restaurant. You can´t just show up and start right away. It takes months to find the right place and the staff."

Gulf Arab powers Saudi Arabia and Qatar have both called for arming the anti-Assad rebels. While they have not yet won wide support for this, light weapons are already being smuggled in.

Some analysts say it is time to arm the rebels to stop radicals from gaining ground. But skeptics say there is no guarantee that rebels will not turn against their benefactors.

Al-Shami, who plans to leave Lebanon to join a rebel unit, is suspicious of outside involvement.

"We don´t want outsiders to lead our revolution, not secular, not Muslim Brotherhood, not Salafists," he said.

But that doesn´t mean they won´t accept help. "We are drowning right now," he said. "If someone reaches out his hand to me, I will take it." (Editing by Giles Elgood) (© Thomson Reuters 2012. 03/29/12)