Mr Obama insisted that the United States has not ruled out any options in dealing with Syria as the United States investigates whether the government of Syrian President Bashar al-Assad used chemical weapons.
But Mr Obama, who has spent much of his presidency winding down wars in Iraq and Afghanistan, made clear he was not inclined to send troops to Syria, saying "I do not foresee" such a scenario.
Leaders in the region that he has consulted on this issue agree with him, Mr Obama said.
If Syria is found to have used chemical weapons, however, Mr Obama will be under pressure to take some action beyond what the United States is already doing. The Obama administration is considering sending lethal aid to Syrian rebels.
Mr Obama, who has come under fire from some critics in Washington who contend he has a muddled approach to Syria, insisted the United States is not standing by even as it waits for a chemical weapons ruling.
"We're not waiting," he said. "We are working to apply every pressure point that we can on Syria."
The United States has said it has "varying degrees of confidence" that chemical weapons have been used by Syria's government, which violates a "red line" that Mr Obama had established against such action.
At his news conference with Costa Rican President Laura Chinchilla, Mr Obama said more evidence is bound to turn up if Syria is continuing to use chemical weapons.
"If in fact there is the kind of systematic use of chemical weapons inside of Syria, we expect we are going to get additional further evidence and at that point we will absolutely present that to the international community," Mr Obama said.
Any additional steps taken by the United States, he said, will be based on the "facts on the ground" in Syria and what is in the best interests of the American people and US national security."
He stressed he would not be pressured prematurely into a deeper intervention into Syria.
"I'm going to make those decision based on the best evidence and after careful consultation, because when we rush into things, when we leap before we look, then not only do we pay a price but oftentimes we see unintended consequences on the ground. So it's important that we do it right," Mr Obama said.
Privately, US officials predict it will be weeks before any conclusion is reached about whether Syria used chemical weapons. Syria denies using chemical weapons.
Obama administration officials have not specified what "physiological" evidence they have that Syrian forces used sarin but US government sources said it included samples of blood from alleged victims, and of soil.
Mr Obama has repeatedly shied away from deep US involvement in the Syrian conflict, which erupted in 2011 and has killed 70,000 people and created more than 1.2 million refugees.
A New York Times/CBS News poll released on Tuesday found that 62 percent of Americans believe the United States has no responsibility to do something about the fighting between Assad's forces and anti-government rebels.
Only 39 percent of respondents said they were following the Syrian violence closely, indicating that it is not among US citizens' top concerns.