By Tom Perry and Laila Bassam

BEIRUT (Reuters) - Syrian President Bashar al-Assad and his allies hope to benefit from Donald Trump’s election win, believing it has saved them from the risks of an interventionist Clinton administration.

Trump's win may have already shifted the course of the Russian-backed military campaign in Aleppo. A senior pro-Assad official told Reuters that plans to capture the rebel-held east by January were shaped around an assumption Clinton would win.

The confidence in Damascus will have been justified if some of Trump’s comments on Syria crystallize into policy, though there are questions over how far he will follow through on suggestions such as cooperating with Russia - President Bashar al-Assad's most powerful military ally - against Islamic State.

One complicating factor could be Trump's tough stance on Iran, Assad's other main military backer. Trump has threatened to rip up the nuclear deal with Iran and heaped criticism on the sanctions relief it brought. Long-standing Republican aversion to Assad may also block any big policy shift, analysts say.

Yet Trump has struck a different tone to current U.S. policy on some aspects of the multi-sided Syrian conflict, where the United States with allies Turkey and Saudi Arabia has backed some of the insurgents who have been fighting to topple Assad for more than five years.

Trump has questioned the wisdom of backing rebels, played down the U.S. goal of getting Assad to leave power, and noted that while he didn't like him, "Assad is killing ISIS" with Iran and Russia. ISIS is an acronym for Islamic State.

"This is very comforting for us and our allies in Syria," said the senior official in the military alliance fighting in support of Assad, who is backed by the Russian air force, Iran's Revolutionary Guards, Lebanon's Hezbollah, and other militias.

"The wave is currently with us, serving our interests, and we must benefit from it as fully as possible," said the official, who declined to be identified by nationality or affiliation so he could give a frank assessment.

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The war has shattered Syria into a patchwork of areas controlled by Assad's state, rebels battling to topple him, a powerful Kurdish militia, and the Islamic State group. It has killed hundreds of thousands of people, and created the world's worst refugee crisis.

While Washington has provided significant support to the opposition, it has never matched the backing given to Assad by Russia and Iran. The rebels have seen U.S. policy as a betrayal of their revolt, with Washington focusing mostly on the fight against IS in the last two years.

TRUMP "A NEW FACTOR" FOR DAMASCUS

The ground war between Assad and the rebellion has this year focused largely on Aleppo, in the north west of Syria. The government is trying to recapture the rebel-held east of the city, the opposition's most important urban stronghold.

Expectations of a Hillary Clinton win have been shaping military planning in the Aleppo campaign for some time, and the aim had been to conclude the campaign before the new U.S. president took office, the senior official said.

While that is still the plan, the official said Trump's victory was a "new factor". Russian President Vladimir Putin would "certainly have a different approach towards the entire Syrian crisis based on what will happen with Trump".

The Syrian newspaper al-Watan said most Syrians had felt "joy" at the result, and that many had spent the night up following the U.S. election. Trump had no designs in Syria, or the region, it declared.

While some in the opposition expressed concern about Trump's statements and views on Putin, others still hold out hope for a U.S. policy that serves their cause. A senior rebel leader noted Trump's views on Iran were "positive" for the Syrian opposition.

"Today, the role of the United States remains active and essential in Syria, regardless of whether he tries to distance himself from it, he won't be able to," said the rebel, who declined to be identified so he could talk freely.

A build-up of Russian forces has fueled speculation of an imminent escalation in the campaign for eastern Aleppo, where hundreds of people were reported killed in air strikes before Russia declared a pause on Oct. 18.

Rebels say they are well-entrenched in eastern Aleppo, a besieged area the United Nations says is home to 270,000 people. The rebels say it will be impossible for government forces to take the area.

Russian firepower has in recent weeks focused on rebel-held areas to the west of the city, from where insurgents recently launched their own offensive on government-held parts of Aleppo. Rebel shelling has killed dozens of people in western Aleppo.

Asked about Aleppo in an October debate with Clinton, Trump said it was a humanitarian disaster but the city had "basically" fallen. Clinton, he said, was talking in favor of rebels without knowing who they were.

The rebels fighting Assad in western Syria include nationalists fighting under the Free Syrian Army banner, some of them trained in a CIA-backed program, and jihadists such as the group formerly known as the al Qaeda-linked Nusra Front.

Rather than focusing on fighting Assad, Islamic State, has prioritized the expansion and defense of its self-declared "caliphate" in eastern and central Syria.

REPUBLICAN AVERSION TO ASSAD, PUTIN, IRAN

Damascus had hoped that it could win back international legitimacy as part of the international fight against Islamic State, but the United States has rejected that idea, viewing Assad as part of the problem.

The U.S.-led fight against Islamic State in Syria is fraught with complications. The United States has built its strategy around a powerful Kurdish militia that has carved out a self-governing areas across much of northern Syria.

But its alliance with that militia, the YPG, has angered Turkey, a U.S. ally worried that Kurdish influence in northern Syria will fuel separatism among its own Kurdish minority.

The YPG has in turn fought FSA rebels backed by Turkey, which is itself waging a major operation in northern Syria.

One senior adviser who Trump will inherit is the chairman of the Joint Chiefs, Marine General Joseph Dunford.

Dunford told Congress in September he thought it would not be a good idea for the military to share intelligence with Russia on Syria, something Moscow has long sought. Republican stalwarts who might join Trump's cabinet or become advisers are unlikely to want close relations with Putin.

Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy, forecast that Trump would start out by sounding out Russia on options for a political transition or agreement to end the war.

Failing that, he may decide to leave western Syria as a Russian zone of influence, with the United States and its allies fighting Islamic State in the east.

"I think it is going to be fluid. Remember a lot of the Republican foreign policy folks in Washington will probably go into this government, and they have very strong feelings about Iran and about the Assad regime, so I don't see a situation where the United States suddenly cozies up to Assad," he said.

(Additional reporting by Yara Bayoumy in Washington; Writing by Tom Perry; editing by Janet McBride)