Speaking from the Rose Garden at the White House, Mr. Obama said the United States must confront Syria, citing intelligence that the Assad regime has used chemical weapons to murder more than 1,400 of its people, including more than 400 children.
"This attack is an assault on human dignity. It also presents a serious danger to our national security. It risks making a mockery of the global prohibition on the use of chemical weapons," Mr. Obama said.
Mr. Obama's move to wait for congressional approval is a surprise. An attack on Syria had been expected any day as punishment for the deadly chemical weapons attack on Syrian civilians.
The White House says it has proof that the Assad regime is behind the attacks. Mr. Obama says the massacre is the worst chemical weapons attack of the 21st century. He recognizes many Americans are weary of war, but says what is happening in Damascus cannot be ignored.
"Yet while I believe I have the authority to carry this military action without specific congressional authorization, I know that the country will be stronger if we take this course, and our actions will be even more effective," the president said.
Congress is on summer vacation until Sept. 9, but some members were expected to head back to the Capitol Saturday night, including Congresswoman Janice Hahn, D-San Pedro. On Sunday they'll learn more about the president's plan of attack.
Hahn says she wrote to the president encouraging him to consult with Congress before taking action.
"I'm not really quite sure what the scope or duration of this military strike would be. I'm not sure what it is we're trying to accomplish, I don't know if we have an endgame in sight," she said. "I think a lot of Americans are remembering Iraq and Afghanistan."
Some in Congress, even fellow democrats, say they don't support a military strike.
"Is this a war? And if it's not a war, if it's a limited war, I've never heard of anything in my entire life. If you're going to fire shells and bomb a community, that's war. And you have to have a declaration of war that Congress should legally, constitutionally, approve it, and I haven't seen that evidence," said Rep. Charles Rangel, D-New York.
So far, the White House has not said what the president intends to do should he fail to win the support of the House and Senate.
Secretary of State John Kerry on Friday said the U.S. had "clear evidence" of a chemical attack by the Syrian regime.
The president has not put a timetable on a possible attack. He believes an order to the military to proceed would be "effective tomorrow, next week or one month from now." The president says ground forces would not be involved.
Retired U.S. Marine Lt. Col. Hal Kempfer agrees the U.S. needs to send a message to Assad to protect our national security and our neighbors in the region.
"What it does is if we don't take action, it may embolden not just Syria, but other countries to possibly use these weapons, and would embolden terrorists to possibly get their hands on these weapons and use them, so there is an imperative to make a clear statement that this will not be permitted," Kempfer said.
At the U.N. Security Council, China and Russia have blocked efforts by the U.S., Britain and France to pass resolutions against Syria. France says it will wait for its parliament and the U.S. Congress to consider military action before launching air strikes.
The president didn't say so, but his strategy carries enormous risks to his and the nation's credibility, which the administration has argued forcefully is on the line in Syria. Obama long ago said the use of chemical weapons was a "red line" that Syrian President Bashar Assad would not be allowed to cross with impunity.
Only this week, British Prime Minister David Cameron suffered a humiliating defeat when the House of Commons refused to support his call for military action against Syria.
Halfway around the world, Syrians awoke Saturday to state television broadcasts of tanks, planes and other weapons of war, and troops training, all to a soundtrack of martial music. Assad's government blames rebels in the Aug. 21 attack, and has threatened retaliation if it is attacked.
By accident or design, the new timetable gives time for U.N. inspectors to receive lab results from the samples they took during four days in Damascus, and to compile a final report. After leaving Syria overnight, the inspection team arrived in Rotterdam a few hours before Obama spoke.
The group's leader was expected to brief Secretary-General Ban Ki-moon on Sunday.
Local Syrian-Americans react to president's announcement
A coalition of groups took to the streets in Downtown Los Angeles on Saturday to protest against military action. Other Syrian families gathered at Aleppo's Kitchen in Anaheim. Some have lost cousins, brothers and many other relatives during the more than two years of civil war in their homeland.
Mr. Obama's decision is a disappointment to many.
"When it comes to humanity, when it comes to children, any human being, especially the leader of the world, Mr. Obama has to be more strong about his position," said Dima Khedraki. "Today, I felt my president is weak."
Even if Congress approves a military strike, some say it's too little, too late.
"The only thing that is going to happen is more destruction and more death," said Mazen Almoukdad. "There is no specific target that is going to come out of this that is positive."
Hassan Twiet of the Syrian American Council lost several relatives in the suspected gas attacks. He says people in Syria fear what will happen if the president waits for congressional approval.
"There's a lot of concerns that this is going to take a little bit more time," he said. "They think this is a step backward. This is another step to give the regimes to advance on the ground and to kill more people."
The Associated Press contributed to this report.