Obama, facing implacable opposition to a military intervention in Syria in the US Congress and from war-weary Americans, termed the Russian proposal to place Syria's chemical weapons under international control as an "encouraging" sign.
He, however, said he would hold off on military action for now to pursue the initiative. Addressing to the nation from the White House, Obama said he would also discuss it with his Russian counterpart Vladimir Putin, who has been opposing any military action against Syria without UN approval.
"It's too early to tell whether this offer will succeed, and any agreement must verify that the Assad regime keeps its commitments," Obama said.
"But this initiative has the potential to remove the threat of chemical weapons without the use of force." Analysts say Obama's 16-minute address was a frank acknowledgement of how radically the political and diplomatic landscape had shifted in just a few days.
Obama also asked the Senate to put off a vote on his request for an authorisation of military force to let the diplomacy play out. He set no timetables for action, but said any deal with Syrian President Bashar al-Assad would require verification that he keeps his word.
Obama again accused Assad, who celebrated his 48th birthday today, of being responsible for gassing to death over 1,000 people, including hundreds of children on August 21.
"When dictators commit atrocities, they depend upon the world to look the other way until those horrifying pictures fade from memory. But these things happened. The facts cannot be denied.
"The question now is what the US, and the international community, is prepared to do about it. Because what happened to those people - to those children - is not only a violation of international law, it's also a danger to our security, he said.
His speech was planned as Obama's final push to win support from a sceptical public and Congress for his planned strike to punish Syria for what US says was the use of chemical weapons against civilians.