The US President said he will seek congressional authority for the use of force, with a debate and vote after Congress returns on September 9.
Despite the delay, Obama told a press conference at the White House the US military stands ready to act as early as today against Syrian leader Bashar al-Assad's regime and he is "prepared to give that order".
He has constitutional authority to act alone, but said it was important for the country to debate military action. He said: "This would not be an open-ended intervention. We would not put boots on the ground. Instead our action would be designed to be limited in duration and scope.
"But I'm confident we can hold the Assad regime accountable for their use of chemical weapons."
Obama said the chemical weapons attack on the outskirts of Damascus on August 21 was "an assault on human dignity" and presented a serious danger to US national security.
He said: "What message will we send if a dictator can gas hundreds of children to death in plain sight and pay no price? Now is the time to show the world that America keeps our commitments. We do what we say and we lead with the belief that right makes might, not the other way round."
Obama had earlier signalled the US planned "limited, narrow" military action after unveiling an intelligence dossier concluding Assad's forces were behind the chemical attack. It was claimed it killed 1429 people.
With action effectively ruled out until Congress returns, it was a big shift from what was perceived to be a looming strike against Syrian targets.
Obama revealed advisers had cautioned against going to Congress, particularly after David Cameron's plans for Britain to join military strikes were voted down by Parliament on Thursday.
The Prime Minister swiftly gave his backing to the US President yesterday with a message on Twitter saying: "I understand and support Barack Obama's position on Syria".
This week Obama, Cameron and other leaders will gather in St Petersburg for the G20, hosted by Russian president Vladimir Putin, a key ally of the Syrian regime.
Obama's move to seek approval from Congress comes in the face of protests from US lawmakers and concerns from war-weary Americans.
A poll last week showed only 20% of Americans believe the US should take action. Obama said: "I'm asking Congress to send a message to the world that we are ready to move as one nation. I have long believed that our power is rooted not just in our military might, but in our example as a government of the people, by the people, and for the people."
UN weapons inspectors yesterday left Syria and travelled to The Netherlands with evidence and samples relating to the suspected attack, which will go to laboratories in Europe for testing.
Ahead of Obama's statement, Putin urged the US not to attack Syrian forces, claiming a failure to present evidence of regime use of chemical weapons was "disrespectful". Putin said the US should present evidence of a chemical attack by Syrian troops to the UN, adding: "If it is not shown, then there isn't any". He added: "I am convinced [the chemical attack] is nothing more than a provocation by those who want to drag other countries into the Syrian conflict."
Putin said the vote by UK MPs against action "shows that in Great Britain, even if it is the USA's main geopolitical ally ... there are people who are guided by national interests and common sense".
US Secretary of State John Kerry said it is essential not to let Syria off with the attack, partly as a sign to those who might consider using chemical weapons. "History would judge us all extraordinarily harshly if we turned a blind eye to a dictator's wanton use of weapons of mass destruction," he said.
Syria's Foreign Ministry repeated the government's denial that it used chemical weapons and said Kerry's accusations were a "desperate attempt" to justify a military strike.
France is expected to join the strikes. President Francois Hollande said: "The chemical massacre cannot and must not go unpunished."
Damascus residents were yesterday preparing for a strike, stocking up on essentials and shuttering homes. Doctors were trying to get supplies of medicine for poison gas victims.
"We worry about another chemical weapons attack should foreign powers carry out the strike, as some kind of revenge," said Abu Akram, a doctor in Arbin, a rebel-held suburb.
Six US warships have been stationed in the eastern Mediterranean. Dozens of UN staff have left Syria and countries including the UK have issued warnings to citizens about travelling to neighbouring Lebanon, base of Hezbollah militants who have sided with the Assad regime in Syria.
Britain's refusal to join in any action is said to have strained the "special relationship" with the US, but yesterday Obama praised the relationship, and was said to have had a "friendly" phone call with Cameron.
A Downing Street spokesman said the prime minister had explained he wanted to build a "consensual approach" in Britain, which Obama said he "fully respected".