US President Barack Obama speaks next to Vice President Joe Biden (R) at the Rose Garden of the White House in Washington, Aug 31, 2013. [Photo/Agencies]

WASHINGTON - US President Barack Obama stepped back from the brink on Saturday and delayed an imminent military strike against Syria to seek approval from the US Congress in a gamble that will test his ability to project American strength abroad and deploy his own power at home.

Before Obama put on the brakes, the path had been cleared for a US assault. Navy ships were in place and awaiting orders to launch missiles, and UN inspectors had left Syria after gathering evidence of a chemical weapons attack that US officials say killed 1,429 people.

But Obama decided to seek the backing of US lawmakers before attacking, as polls showed strong opposition from Americans already weary of wars in Iraq and Afghanistan. Approval will take at least 10 days, if it comes at all.

"Today I'm asking Congress to send a message to the world that we are ready to move as one nation," Obama said in a dramatic shift he announced in the White House Rose Garden.

Obama, whose credibility has been called into question for not punishing the government of Syrian President Bashar al-Assad for earlier poison gas attacks, warned lawmakers they must consider the cost of doing nothing in Syria.

"Here's my question for every member of Congress and every member of the global community: What message will we send if a dictator can gas hundreds of children to death in plain sight and pay no price?" he said.

Obama's approach, which he debated with top aides on Friday night, has left in doubt whether the United States will carry through with the military steps that the president has already approved.

Backing from Congress is by no means assured, with many Democrats and Republicans uneasy about intervening in a distant civil war in which 100,000 people have been killed over the past 2-1/2 years.

Obama's decision to consult with Congress is in line with an argument he has often made for a more collaborative approach to foreign policy in Washington than there was under his predecessor, US President George W. Bush.

But another reason to bring lawmakers into the process is that Obama might be able to share some of the responsibility with Congress if it votes for strikes on Syria that turn badly for Washington.

Lawmakers for the most part welcomed Obama's decision but looked in no hurry to come back to Washington early from their summer recess, which lasts until Sept 9.

"In consultation with the president, we expect the House to consider a measure the week of Sept 9," said John Boehner, the top US Republican and speaker of the House of Representatives. "This provides the president time to make his case to Congress and the American people."

House members are to receive a classified briefing on Sunday from administration officials to hear the case against Syria. Officials briefed senators on Saturday.

British Prime Minister David Cameron, who was unable to persuade the British parliament to back action earlier in the week, welcomed Obama's decision, as did the government of French President Francois Hollande, with whom Obama spoke on Saturday.

In rebel-held areas of Syria, there was a sense of frustration and disappointment.

"God curse everything," said an activist in the rebel-held territory of Idlib, Ahmad Kaddour. "We've become just a game to people. I think this is going to make the situation worse for those of us living here."

A Reuters reporter visited a group of fighters and activists sitting in a home in Aleppo city. They had not watched Obama's speech, and when told of the president's decision, they all agreed it meant there would be no US strike.

"This is the same old hesitancy that the United States have tortured us with since the beginning of the revolution," one said.

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