President Obama on Saturday slowed his march toward military intervention in Syria with the surprise announcement that he would seek authorization from Congress before acting.

The president said in a Rose Garden appearance that he has decided that force against Syria is necessary, but that he would wait until Congress has a chance to debate and vote on the intervention.

"I know that the country will be stronger if we take this course, and our actions will be even more effective," Obama said. "We should have this debate, because the issues are too big for business as usual."

Congressional leaders said Saturday that they would begine debate as soon as lawmakers returned to work Sept. 9, delaying what appeared to be an imminent U.S. military attack against Syrian President Bashar Assad's regime in retaliation for the Aug. 21 chemical weapons attack that killed more than 1,400 of its citizens, including hundreds of children.

Republican House leaders welcomed the news that Obama would seek their approval, saying it would give the administration time to make a case for such action to both lawmakers and the American public.

"Under the Constitution, the responsibility to declare war lies with Congress," House Speaker John Boehner and members of his leadership team said in a statement. "We are glad the president is seeking authorization for any military action in Syria in response to serious, substantive questions being raised."

Even as he announced that he would seek congressional approval, Obama continued to insist he does not need it, that he already had the authority to initiate a strike. The president declined to say what he would do if Congress refused to approve a strike that the White House believes is necessary to deter similar chemical weapons attacks by other regimes in the future.

It is also unclear how long a debate in Congress could delay potential action in Syria, where American warships are already standing by. Obama said he remains ready to order a strike regardless of how long it's delayed.

"The chairman of the Joint Chiefs has informed me that we are prepared to strike whenever we choose," Obama said. "Moreover, the chairman has indicated to me that our capacity to execute this mission is not time-sensitive; It will be effective tomorrow, or next week, or one month from now. And I'm prepared to give that order."

Obama decided to seek congressional approval after suffering several setbacks last week. The British Parliament refused to back the military action of one of its closest allies and the United Nations Security Council was stymied in its efforts to negotiate a response. Moreover, polls show that Americans generally oppose military action in Syria unless Congress approves it.

Obama said he decided to include Congress in the decision-making process only out of respect for the legislature's role in a democracy.

"I've 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," he said.

Even as Obama was speaking at the hastily arranged appearance, his aides were fanning out to deliver two days of classified and unclassified briefings to lawmakers.

Obama also reiterated his claim that any military intervention would be limited in scope and would not involve the use of U.S. troops.

"In a world with many dangers, this menace must be confronted," the president 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.

"Now is the time," he said, "to show the world that we keep our commitments; we do what we say."