"I'll make the best case I can to the American people, as well as the international community" for a military response to evidence that President Bashar Assad's forces used chemical weapons in a mid-August attack on Damascus suburbs, Obama said Friday during a news conference in St. Petersburg, Russia, where he is attending the Group of 20 summit.
"I believe that when you have limited proportional strike like this ... not some long drawn-out affair ... we should be willing to bear that responsibility," Obama said.
"Over 1,400 people were gassed; over 400 of them were children," Obama said. "This is not something we've fabricated, not something we are using as an excuse for military action. I was elected to end wars, not start them."
He did not directly answer several questions about whether he would proceed with a military assault if Congress fails to approve his authorization response.
He said he knew it would be a "heavy lift" taking his authorization request to Congress, where members from both parties in both houses have expressed reluctance to outright opposition to a military response.
The White House released a joint statement by leaders and representatives of Australia, Canada, France, Italy, Japan, South Korea, Saudi Arabia, Spain, Turkey, Britain and the United States at the G20 summit that condemned the chemical weapons attack on Aug. 21.
"The international norm against the use of chemical weapons is longstanding and universal. The use of chemical weapons anywhere diminishes the security of people everywhere. Left unchallenged, it increases the risk of further use and proliferation of these weapons," the statement said.
"We condemn in the strongest terms the horrific chemical weapons attack in the suburbs of Damascus on August 21st that claimed the lives of so many men, women, and children," the statement said. "The evidence clearly points to the Syrian government being responsible for the attack, which is part of a pattern of chemical weapons use by the regime."
Obama said he and Russian President Vladimir Putin -- who has backed Syria, Russia's long-time ally -- about the situation, noting that the two leaders agree on some issues while disagreeing on others.
Obama said he told Putin he didn't expect the two leaders to agree, "although it is possible that after the U.N. inspectors report it may be more difficult for Mr. Putin to maintain his current position."
"But we both agree that the underlying conflict can only be resolved by a political transition" that a delayed international forum in Geneva, Switzerland, sponsored by Russia and the United States needs to move forward.
"Even if we disagree on this important issue," Obama said, "we must remain together to urge all parties in conflict" to try to resolve it through political measures, not military ones.
Asked if he was fast-tracking military action at the expense of other options, Obama said he was listening to "all ideas."
"I want to repeat it, my goal is to maintain the international norm on banning chemical weapons. I want that enforcement to be real, to be serious," Obama said.
Assad must understand that "gassing innocent people ... delivering chemical weapon against children is not something we do. It's prohibited in active wars between countries. We certainly don't do it against kids. We've got to stand up for this principle."
If there are non-military tools to accomplish this goal, Obama said his preference would be to use them.
He also repeated his desire to work through the U.N. Security Council, noting its "paralysis" on the matter. Russia has vetoed anti-Syria resolutions considered by the council.
"I'm not itching for a military action," he said, adding that so far he hasn't seen any idea that "as a practical matter would do the job."
He said he would consult with its international partners and listen to Congress.
"Failing to respond to this breach of this international norm would send a signal to rogue nations, authoritarian regimes and terrorist organizations, that they can develop and use weapons of mass destruction and not pay a consequence," Obama said. "And that's not the world that we want to live in."