By Steve Holland and Matt Spetalnick
ST. PETERSBURG, Russia (Reuters) - President Barack Obama said on Friday that most leaders of the G20 countries agree that Syrian President Bashar al-Assad is responsible for using poison gas against civilians as the U.S. leader tried to rally support at home and abroad for a military strike.
"I was elected to end wars, not start them," Obama said at a news conference in Russia. "I've spent the last four and a half years doing everything I can to reduce our reliance on military power as a means of meeting our international obligations and protecting the American people.
"But what I also know is that there are times where we have to make hard choices if we're going to stand up for the things that we care about. And I believe that this is one of those times."
At a meeting of the Group of 20 leading economies, the American president won some support but no consensus for limited U.S. strikes on Syria in response to a chemical attack last month outside Damascus that he said killed 1,400 people, 400 of them children.
Obama also faces an uphill battle at home, where he planned to discuss Syria in an address to the American public on Tuesday.
He said G20 leaders agreed that chemical weapons were used in Syria and that the international ban on chemical weapons needs to be maintained. Ten G20 countries plus Spain supported a "strong international response," the White House said later.
However, Obama said there was disagreement about whether force could be used in Syria without going through the United Nations. The United States has been unable to win U.N. Security Council approval for military action against Syria because of the opposition of veto-wielding Russia.
A number of countries believed that any military force needed to be decided at U.N. Security Council, a view he said he does not share.
"Given Security Council paralysis on this issue, if we are serious about upholding a ban on chemical weapons use then an international response is required, and that will not come through Security Council action," he said.
The decision to strike Syria, especially after long and costly U.S. wars in Iraq and Afghanistan, is unpopular in the United States as well. Obama planned to give an address on Syria on Tuesday as Congress considers his request for limited military action against Assad's government.
"I do consider it part of my job to help make the case and to explain to the American people exactly why I think this is the right thing to do," he said.
Obama said the United States has frequently had reservations about getting involved in conflicts far from its shores, including whether to help Britain at the start of World War Two.
The U.S. decision to intervene in the Kosovo conflict in 1999 was initially unpopular but was ultimately "the right thing to do," Obama said.
Obama argued that even though strife in Syria is far away, it has a potential to affect Americans in the long run.
"I think that the security of the world and my particular task looking out for the national security of the United States requires that when there's a breach this brazen of a norm this important and the international community is paralyzed and frozen and doesn't act, then that norm begins to unravel," Obama said.
"And if that norm unravels, then other norms and prohibitions start unraveling. And that makes for a more dangerous world. And that, then, requires even more difficult choices and more difficult responses in the future."
Obama declined to say whether he would go it alone with a military action if Congress fails to give him the green light.
(Corrects to show countries backing strong response Friday not all G20 members)
(Additional reporting by Roberta Rampton and Mark Felsenthal; Editing by Doina Chiacu)