"Over the last several days, we have heard from members of Congress who want their voices to be heard," Obama said. "I absolutely agree."
Just minutes after Obama's statement, the Syrian army recommenced its shelling of rebel-held Damascus suburbs, which had halted for several hours.
In his statement, Obama condemned Assad's regime, describing the alleged chemical attack as "an assault on human dignity" that "presents a serious danger to our national security." He had previously characterized the use of chemical weapons as a "red line" Assad should not be permitted to cross.
Obama pledged that any military involvement would be of "limited duration and scope."
"This would not be an open-ended intervention," he said. "We would not put boots on the ground."
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Before revealing he would seek approval from Congress, the President made clear that "we are prepared to strike whenever we choose."
Strikes would be "effective tomorrow or next week or one month from now," Obama said, adding that he is "prepared to give that order."
And yet many rebel groups aligned with the opposition to Assad expressed dismay with the apparent postponement of military intervention. One rebel spokesman told NBC News: "President Obama is sending contradictory messages. He promised to help, and now promises delays."
(Read more: UN weapons inspectors pull out of Syria early)
"If Congress votes against a military action," the spokesman said, "it will mean the American people don't want to help the Syrian people."
Secretary of State John Kerry on Saturday afternoon spoke with Syrian Opposition Coalition President Ahmed Assi al-Jarba to "underscore President Obama's commitment to holding the Assad regime accountable," according to a statement from a senior State Department official.
Key Republican leaders, including House Speaker John Boehner (R-OH) and Majority Leader Eric Cantor (R-Va.), issued a joint statement Saturday afternoon, applauding the President's decision to take his case for intervention to their official chambers.
"Under the Constitution, the responsibility to declare war lies with Congress," they said. "We are glad the president is seeking authorization for any military action in Syria in response to serious, substantive questions being raised."
Congress is slated to return from its five-week recess on Sept. 9.
The window for a potential U.S. attack on Syria opened as United Nations inspectors departed the anxious country ahead of schedule Saturday, less than a day after Kerry delivered a forceful speech arguing America had a moral obligation to punish Assad's regime.
The possibility of U.S. strikes in the hours or days ahead cast a shadow over Damascus. As the army continued its shelling of rebel enclaves throughout the region — suspending only for a few hours before Obama's statement — citizens fretted about the skyrocketing price — or sudden absence — of food, gasoline, and medical supplies. The city was checkered by roadblocks, and traffic was slowed to a crawl.
Activists in the Syrian capital told NBC News that people in some Damascus neighborhoods waited seven hours on bread lines, and scooped up other essential items like rice, tea, and sugar in preparation for a strike. Some people who live in close proximity to possible targets like military installations and barracks have moved, the activists said.
(Read more: War games: What a US strike would look like)
Kerry on Friday made an impassioned case for U.S. military action against Syrian President Bashar al-Assad's regime. Kerry argued that America has a moral obligation to punish Syria for allegedly using chemical weapons.
President Obama says he's comfortable with his decision on Syria, but will seek congressional approval before taking any military action.
"History would judge us extraordinarily harshly if we turned a blind eye to a dictator's wanton use of weapons of mass destruction against all warnings, against all common understanding of decency," Kerry said, after referring to Assad as a "thug and a murderer."
Kerry later said: "The world's most heinous weapons must never again be used against the world's most vulnerable people."
The White House released an intelligence report as Kerry spoke on Friday claiming "high confidence" that the Syrian regime had deployed chemical weapons. The report cited a "large body of independent sources" but acknowledged that not all the evidence of the alleged attack could be declassified. The information released by the government said the attack, carried out last week in the suburbs of Damascus, killed some 1,429 Syrians, including at least 426 children.
"Instead of being tucked safely in their beds at home," Kerry said, "we saw rows of children lying side by side, sprawled on a hospital floor, all of them dead from Assad's gas and surrounded by parents and grandparents who had suffered the same fate."
The Obama administration faces fierce opposition from many members of the U.S. Senate and wide swaths of the American public reluctant to become entangled in a Middle Eastern conflict just a decade after the U.S. invasion of Iraq.
Prior to Kerry's remarks, an NBC News poll showed that nearly 80 percent of Americans believed Obama should get a stamp of congressional approval before using force in Syria. Fifty percent of Americans believe the U.S. should not intervene altogether, according to the poll.
Diplomatic and political tensions heightened early Saturday as it became clearer that the U.S. may be prepared to bring the confrontation to a climax, despite a chorus of opposition from global partners and domestic constituents.
Sen. John McCain (R-Ariz.) decried Obama's plans for limited air strikes on Syria as "cosmetic" during an interview with Jay Leno on "The Tonight Show" on Friday, saying the failure of the U.S. to intervene in the country's bloody, brutal civil war was "shameful."
"The president apparently wants to have a kind of cosmetic strike, launch a few missiles and then say, 'Well, we responded.' This is the same president that, two years ago, said Bashar Assad had to go," McCain said.
Russian President Vladimir Putin meanwhile called on Obama not to act hastily, saying that while he was convinced last Wednesday's lethal chemical attack was "just a provocation of those who want to drag other countries into a Syrian countries," he believes U.S. officials should present any evidence to the contrary to the U.N. inspectors and the U.N. Security Council.
"If there is evidence, it must be provided," Putin said Saturday. "If they are not provided, that means it's not there."
Putin is one of Assad's stalwart allies, and holds veto power in the U.N. Security Council, which accounts for why Kerry did not take his forceful case for military intervention there. The Russian leader's remarks were his first public comments on the unfolding crisis since the alleged Aug. 21 attack.
Britain, the most steadfast U.S. ally, rejected military action in a stunning vote Thursday night, delivering a dramatic blow to the Obama administration and thwarting any attempt to build a robust coalition of Western powers.
An administration official confirmed that Obama spoke Friday with British Prime Minister David Cameron as well as French President Francois Hollande, who has come out in support of international military action against the Assad regime.
The chemical attack "must not go unpunished," Hollande told the French newspaper Le Monde. "Otherwise, it would be taking the risk of an escalation that would normalize the use of these weapons and threaten other countries."
Senior U.S. officials Saturday will hold unclassified conference calls with the Senate Republican Conference and the Senate Democratic Caucus to continue consultations on potential U.S. military action, according to a White House official.
Secretary of Defense Chuck Hagel and Chairman of the Joint Chiefs of Staff General Martin Dempsey arrived at the White House on Saturday morning, a U.S. official confirmed.
All members of the House of Representatives have been invited to an in-person classified briefing regarding the Syria crisis on Sunday, according to an email sent to the House Republican Conference. The classified assessment on Syria was delivered to the Capitol on Friday night, the email to legislators said.
The U.N. weapons inspectors had spent three days this week traveling through violence-hit areas near Damascus and a fourth day meeting with patients at a government-run hospital. They concluded their investigation Friday and left Syria on Saturday through Lebanon.
The team of inspectors will begin "collating" soil samples collected during the investigation on Sunday, U.N. spokesman Martin Nesirky said at a press briefing Saturday.
Nesirky said that the notion that the early exit of the inspectors clears the path for U.S. strikes is "grotesque."
—By Daniel Arkin and Kristen Welker of NBC News. CNBC contributed to this report.