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* The key to reducing political damage: Keep intervention short
* Skeptical public could rally around troops in military action
* 'Doing nothing ... would be devastating' - analyst
By John Whitesides
WASHINGTON, Aug 28 (Reuters) - Most Americans want no part of a U.S. military intervention in Syria, but there is a growing sense in Washington that President Barack Obama would face more political risks from a weak response to Syria's use of chemical weapons than from an attack on Bashar al-Assad's government.
As Obama's administration builds a case for a likely military action in Syria, several analysts said such a move probably would not have lingering negative consequences for the president at home - as long as the intervention was short-lived.
By declaring last year that Assad would cross a "red line" that could trigger a U.S. response if he used chemical weapons, Obama ensured that foreign foes and allies - as well as his Republican political rivals - would view any failure to respond as a sign of presidential weakness.
"Obama has to consider the implications for other policy areas if he fails to act," said William Galston, a senior fellow at the Brookings Institution, who was a domestic policy adviser to President Bill Clinton. "Doing nothing - that is what would be devastating."
After the chemical attack near Damascus last week that killed hundreds of Syrian adults and children and injured many more, Obama "doesn't have that luxury," of inaction, he said.
Obama, who has long been wary of any involvement in Syria's civil war, and U.S. allies appeared on Tuesday to be carefully laying the groundwork for a coordinated military response.
POLLS SHOW SINKING SUPPORT FOR INTERVENTION
Polls show large majorities of Americans, weary of more than a decade of wars in Iraq and Afghanistan, strongly oppose a U.S. military mission in Syria. A Reuters-Ipsos poll last week found about 60 percent of Americans are against U.S. intervention in Syria, while just 9 percent support it.
More Americans favor intervention if Syria has used chemical weapons, but even that support has dipped as the situation in Syria has deteriorated, according to the poll.
However, U.S. military action typically sparks a surge of at least short-term support for their president's actions, as Americans rally around the troops.
"My prediction would be that public opinion would swing very quickly to support the military action in Syria," said Ipsos pollster Julia Clark. "The danger for Obama is if it becomes more prolonged."
On Capitol Hill, lawmakers have been sending mixed signals on Syria, arguably giving Obama more room to maneuver.
Republicans, led by Senator John McCain of Arizona, have criticized Obama for moving too slowly and called for a strong military intervention.
McCain suggested on Tuesday that a brief attack by cruise missiles, aimed more at sending a message to Assad than altering the course of Syria's civil war, could make the situation worse by allowing an emboldened Assad to claim that he had withstood an assault by the Americans.
Meanwhile, some liberal Democrats and conservative Republicans - including Senator Rand Paul of Kentucky, a potential 2016 presidential candidate - have opposed any U.S. intervention.
NO 'LASTING' POLITICAL IMPACT
Obama faces the decision on Syria just as Congress prepares to return to Washington next week to renew a lingering budget fight over government spending and the federal debt limit.
Some Republicans are threatening another government shutdown if Democrats don't agree to deeper spending cuts, or to delay funding for the president's healthcare overhaul.
The intense focus in Congress on domestic policy issues means the impact of any short-term military action in Syria could be limited.
"It's one of those things that, however tragic, won't have any lasting political impact one way or the other," Republican strategist Rich Galen said of a short-term U.S. intervention in Syria.
"We are locked in a cycle of domestic turmoil, and politically that will overwhelm everything else." (Additional reporting by Patricia Zengerle; Editing by David Lindsey and Peter Henderson; desking by Christopher Wilson)