WASHINGTON (Reuters) - As the Obama administration weighs worst-case scenarios for Syria, one stands out: a civil war that develops into a proxy battle between Arabs and the West on one side, and Russia and Iran on the other.
U.S. officials stress they do not want to play a military role in Syria, where President Bashar al-Assad's crackdown on protests has killed more than 5,000 people and raised fears of a protracted power struggle in a country at the heart of the Arab world.
But after U.S. and Arab-led efforts to craft consensus in the U.N. Security Council on Syria's political transition were torpedoed by vetoes from Russia and China, some analysts say risks are growing that the international community will line up on opposite sides of a fratricidal war.
The volatile ingredients are already in place.
Resistance fighters known as the Free Syrian Army have pledged to liberate the country from Assad's rule. Activists call for armed support for rebels. And Syrian security forces are ratcheting up the violence, vowing to fulfill their president's threat to strike with an "iron fist" against the government's opponents.
""There is a risk of it could become a proxy conflict. It is already headed in that direction," said Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy.
"I think you will see now different countries in the region betting on the Free Syrian Army. Already weapons have been coming in from Lebanon. You will now see more coming in from Jordan, from Turkey, from Iraq or from Russia. Everyone will start to operate in this environment."
U.S. officials say their emphasis is on building support for Syria's beleaguered political opposition and possibly providing humanitarian relief for refugees as the fighting intensifies.
For their part, Russia and Iran say they are urging Damascus to make reforms. But they reject what they describe as a Western-engineered attempt to overthrow the government of one of their closest allies.
Some in Washington worry the situation may eventually edge toward a Cold War-style proxy conflict.
"At the moment it is not something that is being discussed," one U.S. official said on condition of anonymity. "That is not to say that at some point down the line it won't be."
During the Cold War, Washington and Moscow fought proxy battles in Latin America, Africa, Afghanistan and elsewhere, arming allied governments or insurgents fighting against them.
U.S. President Barack Obama, facing re-election in November,
has steered away from deeper involvement in Syria, a complex and combustible political puzzle that is a potential threat to U.S. allies including Israel, Turkey and Jordan.
"It is very important for us to try to resolve this without recourse to outside military intervention. And I think that's possible," Obama told NBC this week, dismissing parallels with the international military effort that toppled Libya's Muammar Gaddafi last year.
But Damascus, facing its greatest crisis in four decades of the Assad family's dynastic rule, contends that it is already fighting an Islamic insurgency funded and directed by enemies in U.S.-allied Gulf Arab states.
Turkey, which shares a long border with Syria, has expressed outrage at the violence and floated the idea of "humanitarian corridors" to stem the bloodshed. Western powers including the United States and the European Union have imposed economic sanctions to pressure Assad and isolate his government. Obama has called on Assad to step down.
Russia, which sells Syria arms and maintains a military base on its Mediterranean coast, has shown no sign of backing away from its Syrian alliance.
Foreign Minister Sergei Lavrov visited Damascus on Tuesday and emerged saying that Assad was committed to halting the violence and would soon roll out new political reforms, promises the Syrian leader has reneged on in the past.
Iran has also stood by Syria, which has long helped it support the militant anti-Israel Hezbollah faction in neighboring Lebanon, and accused Washington of trying to destabilize the region.
"America's plans for Syria are evident and unfortunately some foreign and regional countries take part in America's plans," Iranian Supreme Leader Ayatollah Ali Khamenei said late last month.
Washington's plan for Syria thus far appears limited. After Russia's and China's double veto in the U.N. Security Council, Secretary of State Hillary Clinton on Sunday suggested the United States would work with allies to tighten sanctions and support democratic change in Syria even without Security Council backing.
But many analysts say expanding violence on the ground may eventually force Washington and its allies to consider additional steps - which would be fraught with political risk even if no foreign forces were directly involved.
"I think we should be helping them, and I think we should look at ways we can help them," Republican Senator John McCain said on Tuesday, suggesting that any new working group on Syria should consider all options including military assistance.
"I think everything should be on the table as to what would be the most effective in bringing this massacre to a halt."
State Department spokeswoman Victoria Nuland said the United States did not believe arming the opposition was a solution.
"We don't think (sending) more arms into Syria is the answer," Nuland said. "The answer is to get to a national democratic dialogue for the violence to stop for the regime's tanks to come out of the cities, and then for monitors to be able to go back in."
Shadi Hamid, a Middle East expert at the Brookings Doha Center, said this might be wishful thinking.
"I just don't see the Syrian regime giving up here. I think they are going to fight this to the very last drop of blood, and that doesn't make me optimistic about a political solution," said Hamid, who argues that the international community should be more proactive about possible military intervention.
Not all experts are persuaded that a proxy conflict is the cards, pointing to the political risks for Obama and a U.S. public weary of long conflicts in both Iraq and Afghanistan.
And U.S. fears over a Syrian quagmire may find an echo in Moscow, where the immediate push to thwart U.S. objectives at the United Nations may not translate into lasting support for Assad's government, according to Anthony Cordesman, a senior analyst at the Center for Strategic and International Studies.
"There are Russian interests at stake, but not vital Russian interests," Cordesman said.
"Russia should certainly be trying to find a way to handle this issue which shows that Russia has the influence to be decisive. But they also want to see broad stability."
Reporting By Andrew Quinn; additional reporting by Susan Cornwell