By Steve Holland and Matt Spetalnick
STOCKHOLM (Reuters) - President Barack Obama issued a blunt challenge to sceptical U.S. lawmakers on Wednesday to approve his plan for a military strike on Syria, saying inaction would put America's prestige and their own credibility at risk.
Using a visit to Sweden to build his case for military action, Obama insisted that the world could not remain silent after the "barbarism" of the August 21 chemical weapons attack he blamed on the forces of Syrian President Bashar al-Assad.
"My credibility is not on the line. The international community's credibility is on the line," Obama told a news conference in Stockholm.
"And America and Congress' credibility is on the line, because (otherwise) we give lip service to the notion that these international norms are important."
One day before travelling to St. Petersburg for a G20 summit hosted by Vladimir Putin where Obama will look to persuade other world leaders over Syria, he said he held out hope that the Russian president would back away from his support for Assad.
Obama's comments came after Putin offered a glimpse of potential compromise over Syria by declining to entirely rule out Russian backing for military action. At the same time, Putin said any strike on Syria would be illegal without U.N. support.
Obama has taken a big political gamble by delaying military action and asking a divided Congress to grant authorisation for a strike on government targets in Syria.
Although Obama denied it, foreign policy experts say his standing as a world leader is also at stake if he fails to enforce his year-old warning to Assad.
Obama appeared to take umbrage at a reporter's question about the "red line" he set for Assad at an August 2012 White House news conference.
"I did not set a red line, the world set a red line," Obama said, referring to bans on chemical weapons use.
WILL OBAMA ACT ALONE?
Obama declined to say if he would proceed with a strike even if Congress rejected the plan. But he said he was not required by law to put the matter before Congress and made clear he reserved the right to act to protect U.S. national security.
"I would not have taken this before Congress just as a symbolic gesture," he said, as he made some of the strongest hints so far that he could act on his own if he chose that course.
At the joint news conference with Prime Minister Fredrik Reinfeldt, a Swedish reporter asked how it felt to be a Nobel Peace Prize winner preparing to attack Syria.
"I would much rather spend my time talking about how every 3- and 4-year-old gets a good education, than I would spending time thinking about how I can prevent 3- and 4-year-olds from being subjected to chemical weapons and nerve gas," he replied.
Obama will fly to Russia on Thursday for a two-day summit of the Group of 20 leading economies, a gathering sure to be dominated by tensions over Syria. The meetings will bring him face-to-face with Putin, a key Syrian ally and arms supplier and a staunch critic of the U.S. push for military action.
"Do I hold out hope that Mr. Putin may change his position on some of these issues? I'm always hopeful, and I will continue to engage him," Obama told reporters.
Syria tops the list of disputes that have sent U.S.-Russian relations to one of their lowest points since the end of the Cold War.
Obama's three-day foreign trip offers a chance to try to shore up a shaky international coalition against Syria.
Britain, a generally reliable U.S. ally, pulled out after a parliamentary revolt last week, but France, western Europe's other main military power, is still coordinating possible action with the Pentagon.
Obama will meet French President Francois Hollande, Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe on the G20 sidelines.
Reinfeldt's government is close to the United States on many issues, but he made clear that Sweden had no intention of assisting in military action, saying: "let's put our hope into the United Nations."
Although the Nordic democracies generally do not command heavy U.S. foreign policy attention, Obama was expected to make his case on Syria at a dinner with regional leaders.
Any attack on Syria is likely on hold until at least next week, the earliest timeframe for a vote by U.S. lawmakers, who formally reconvene on September 9 after their summer break.
Obama faces a tough fight in Congress for endorsement of strikes over what Washington says was the killing of 1,400 people in a chemical attack carried out by Assad's forces.
Many lawmakers staunchly oppose a strike, fearing it would entangle the United States in the Syrian civil war. Others favour rewriting the use-of-force resolution the White House sent to Capitol Hill over the weekend so that it sets clear limits on any military action.
Still others, mostly more hawkish Republicans, want Obama to make sure any strike is punishing enough to weaken the Syrian military, and are calling for increased help for beleaguered anti-Assad rebels.
(Additional reporting by Geert De Clercq, Alistair Scrutton, Niklas Pollard, Simon Johnson, Anna Ringstrom in Stockholm and Roberta Rampton in Washington; Writing by Matt Spetalnick; Editing by Mark Trevelyan and Robin Pomeroy)