President Obama said the issue was of concern not only to Washington but also to its close allies in the region, including Israel.
Seeking re-election in November, Obama has been reluctant to get the United States involved in another war in the Middle East, even refusing to arm rebels fighting a 17-month-old uprising against Assad.
Syria last month acknowledged for the first time that it had chemical and biological weapons and said it could use them if foreign countries intervene - a threat that drew strong warnings from Washington and its allies.
Western countries and Israel have expressed fears chemical weapons could fall into the hands of militant groups as Assad's authority erodes.
Israel has said that if Syrian-backed Hezbollah guerrillas used the situation to take control of the weapons, it would "act immediately and with utmost force."
"We're monitoring that situation very carefully. We have put together a range of contingency plans," President Obama said when asked whether he envisioned the possibility of using U.S. forces at least to safeguard Syria's chemical arsenal.
The Global Security website, which collects published intelligence reports and other data, says there are four suspected chemical weapons sites in Syria: north of Damascus, near Homs, in Hama and near the Mediterranean port of Latakia. Weapons produced include the nerve agents VX, sarin and tabun, it said, without citing its sources.
President Obama also used the opportunity to renew his call for Assad to step down.
"The international community has sent a clear message that rather than drag his country into civil war, he should move in the direction of a political transition," said Obama. "But at this point, the likelihood of a soft landing seems pretty distant."
President Obama said the United States had already provided $82 million in humanitarian assistance for Syrian refugees and will "probably end up doing a little bit more" to keep the situation from destabilizing Syria's neighbors.
Intellpuke: You can read this Reuters article in context here: www.guardian.co.uk/world/2012/aug/20/barack-obama-syria-chemical-weapons