Obama said Washington was "looking at the possibility of a limited, narrow act" and there would be no "long-term campaign".
"We're not considering any open ended commitment. We're not considering any boots on the ground approach," Obama told reporters yesterday. He emphasised that he had "not made any decisions" about what actions the US will take.
He said whatever the US does, it would not be a major operation. "We have consulted with allies. We have consulted with Congress," Obama said, indicating an attack on Syria is imminent.
Emerging from a situation room meeting headed by Obama, Secretary of State John Kerry confirmed that the US would not seek approval of the UN Security Council for an attack because of the opposition from Russia to the use of military force.
"Because of the guaranteed Russian obstructionism of any action through the UN Security Council, UN cannot galvanise the world to act as it should," he said.
United Nations weapons inspectors left Syria for Lebanon today and were expected to brief Secretary-General Ban Ki-moon.
Ban has said he will present their findings to the UNSC, but he wants to wait until a final report is completed. It could take as long as a week, officials said.
US leaders indicated that they had adequate information about the use of chemical weapons and were determined to act.
"I have said before, and I meant what I said, that the world has an obligation to make sure that we maintain the norm against the use of chemical weapons," Obama said.
Kerry laid out a raft of what Washington said was a "high confidence" intelligence assessment about the attack.
The main findings of the released unclassified summary stated that the attack by President Bashar al-Assad's regime on August 21 killed 1,429 people, including 426 children, and Syrian military chemical weapons personnel were operating in the area three days before the incident.
Communications were intercepted involving a senior Damascus official who "confirmed chemical weapons were used", the summary said.
In response, Syria's state-run SANA news agency said Kerry was using "material based on old stories which were published by terrorists over a week ago".
Russia, a key ally of Syria, has warned that "any unilateral military action bypassing the UN Security Council" would be a "direct violation of international law".
Russia, along with China, has vetoed two previous draft resolutions on Syria.
The US was also dealt a blow on Thursday when the UK parliament rejected a motion supporting military intervention. The vote ruled the UK out of any potential military alliance.
British Prime Minister David Cameron and Obama spoke over the telephone yesterday, agreeing to continue to cooperate on international issues. The President told Cameron he "fully respected" the approach taken by the UK government.
US officials said they would continue to push for a coalition, and France said it was ready to take action in Syria alongside the US.
Both Germany and Canada have ruled out joining any military strikes against Syria while French President Francois Hollande has said the British decision would not affect his government's stance.
Obama and Hollande discussed the issue in a telephone conversation yesterday. Both leaders wanted to send Damascus a "strong message" to condemn the alleged use of chemical weapons.
Neither France nor the US needs parliamentary approval for military action.
Another US ally, Turkey, called for action similar to the NATO bombing raids in the former Yugoslavia in 1999.
NATO carried out 70 days of air strikes to protect civilians from attack in Kosovo, despite not having a UN resolution.
Turkish Prime Minister Recep Tayyip Erdogan also said that any military intervention should be aimed at toppling Assad.
Protests were taking place around the world against the possible US military strike on Syria.