Speaking at a joint White House news conference with South Korea President Park Geun-hye, Obama said those dual concerns also come into play in "ensuring that we've got a stable Syria that is representative of all the Syrian people, and is not creating chaos for its neighbors."
He said to that end his administration has exerted pressure on Syrian President Bashar Assad to leave power, provided humanitarian aid to Syrian civilians, helped the rebel opposition and mobilized the international community to isolate Syria.
"That's why we are now providing non-lethal assistance to the opposition, and that's why we're going to continue to do the work that we need to do," Obama said.
"And in terms of the costs and the benefits, I think there would be severe costs in doing nothing. That's why we're not doing nothing. That's why we are actively invested in the process."
He said his administration is re-evaluating what actions to take "in conjunction with other international partners" on a regular basis.
"I think that, understandably, there is a desire for easy answers. That's not the situation there," Obama said. "And my job is to constantly measure our very real and legitimate humanitarian and national security interests in Syria, but measuring those against my bottom line, which is what's in the best interest of America's security and making sure that I'm making decisions not based on a hope and a prayer, but on hard-headed analysis in terms of what will actually make us safer and stabilize the region."
Obama addressed the issue of "perceived" violations of the "red line" by the Syrian government, which allegedly has used chemical weapons against its people.
"The operative word there, I guess ... is 'perceived.' And what I've said is that we have evidence that there has been the use of chemical weapons inside of Syria, but I don't make decisions based on 'perceived,'" he said. "And I can't organize international coalitions around 'perceived.' We've tried that in the past, by the way, and it didn't work out well."
That apparently was a veiled reference to the decision by his predecessor, George W. Bush, to wage war in Iraq on the presumption Iraqi leader Saddam Hussein had weapons of mass destruction he intended to use.
"We want to make sure that we are acting deliberately. But I would just point out that there have been several instances during the course of my presidency where I said I was going to do something and it ended up getting done. And there were times when there were folks on the sidelines wondering why hasn't it happened yet and what's going on and why didn't it go on tomorrow? But in the end, whether it's [slain al-Qaida leader Osama] bin Laden or [deposed Libyan strongman Moammar] Gadhafi, if we say we're taking a position, I would think at this point the international community has a pretty good sense that we typically follow through on our commitments."
White House spokesman Jay Carney told reporters Monday the administration doubted claims by Carla Del Ponte of a U.N. commission looking into human rights abuses in Syria rebel forces might have used the nerve agent sarin.
"We are highly skeptical of any suggestions or accusations that the opposition used chemical weapons," Carney said. "We find it highly likely that chemical weapons, if they were, in fact, used in Syria -- and there is certainly evidence that they were -- that the Assad regime was responsible."
Del Ponte, a former chief prosecutor for international criminal tribunals that investigated Rwanda and the former Yugoslavia, told Swiss-Italian TV Sunday there were "strong, concrete suspicions" rebels had used the poison gas.
The rebels denied it and the commission pulled back from Del Ponte's remarks Monday.
"The Independent International Commission of Inquiry on the Syrian Arab Republic wishes to clarify that it has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict," the commission said in a statement.
NATO Secretary-General Anders Fogh Rasmussen told reporters in Brussels chemical weapons appear to have been used in Syria, but he said the evidence was not clear who was responsible.
"We do not have confirmed, consolidated information as to who might have used" chemical weapons, he said.
Rasmussen echoed the Obama administration's insistence on a careful approach to outside involvement in the Syrian conflict.
"It is of utmost importance to get consolidated information, to get clear evidence," he said.
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