* "We need a coalition," French minister says
* Obama's announcement creates "a new situation" - Valls
* Delay allows Assad to prepare for strikes - rebel
* Some Syrian activists believe strike will never happen
By Alexandria Sage and Roberta Rampton
PARIS/WASHINGTON, Sept 1 (Reuters) - France said on Sunday it could not act alone against Syria after the United States stepped back from the brink, making Paris the last remaining top ally in the Western coalition to hesitate over punishing President Bashar al-Assad.
After President Barack Obama delayed an imminent strike by deciding to consult Congress and the British parliament vetoed any involvement, French Prime Minister Jean-Marc Ayrault is to discuss with senior lawmakers on Monday how to respond to allegations chemical weapons attacks were launched by Assad.
Interior Minister Manuel Valls said France would await the U.S. Congress's decision, which is unlikely for more than a week at least. "France cannot go it alone," Valls told Europe 1 radio. "We need a coalition."
Obama made the surprise announcement on Saturday that he would seek approval from Congress for military intervention 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 U.S. assault. Navy ships were in place and awaiting orders to launch missiles, and U.N. inspectors had left Syria after gathering evidence of a chemical weapons attack that U.S. officials say killed 1,429 people.
Valls said Obama's announcement had created "a new situation" which meant France would have to wait "for the end of this new phase".
France, which ruled Syria for more than two decades until the 1940s, has, like the United States and Britain, the military strength to blitz the country in response to the Aug. 21 attack on rebel-held areas around Damascus. The Syrian government has accused the rebels of being to blame for the poison gas attack.
President Francois Hollande reaffirmed to Obama on Saturday his will to punish Syria but has come under increasing pressure to put the intervention to parliament.
A BVA poll on Saturday showed most French people do not approve of military action against Syria and most do not trust Hollande to conduct such an operation.
His prime minister is scheduled to meet the heads of the two houses of the French parliament and the conservative opposition on Monday before a parliamentary debate on Wednesday.
Last month's attack was the deadliest incident of the Syrian civil war and the world's worst use of chemical arms since Iraq's Saddam Hussein gassed thousands of Kurds in 1988.
However, polls also show strong opposition to a strike on Assad's forces among Americans weary of wars in Iraq and Afghanistan. Congressional approval will take at least 10 days, if it comes at all.
A senior Syrian rebel expressed concern about the delay, saying it gave Assad and his government the chance to keep killing and prepare from a missile or bomb attack.
"As days go by, more people get killed by the hands of this regime. Further delay for action gives them a chance to change the position of their weapons," said Mohammad Aboud, the Deputy Commander of eastern joint command of the Free Syrian Army.
"According to the intelligence that we have, we know that he exploits this delay to prepare for this strike," Aboud, a lieutenant who defected from Assad's forces, told Reuters.
Foreign Ministers from the Arab League, which blamed Syria for the chemical attack but has so far stopped short of explicitly endorsing Western military strikes, are due to meet in Cairo on Sunday.
Obama, whose credibility has been called into question for not punishing Assad over earlier alleged gas attacks, warned lawmakers they must consider the cost of doing nothing in Syria.
"Today I'm asking Congress to send a message to the world that we are ready to move as one nation," he said in the White House Rose Garden.
"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?"
Obama's approach 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.
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.
British Prime Minister David Cameron, who was unable to persuade the British parliament to back action last week, welcomed Obama's decision.
The team of U.N. experts arrived in the Netherlands on Saturday carrying evidence and samples relating to the attack. They had flown from Beirut after crossing the border into Lebanon by road earlier in the day.
The 20-member team had arrived in Damascus three days before the attack to investigate earlier accusations of chemical weapons use. After days holed up in a hotel, they visited the sites several times, taking blood and tissue samples from victims and from soldiers at a government hospital.
Syria and its main ally, Russia, say rebels carried out the gas attack as a provocation. Moscow has repeatedly used its U.N. Security Council veto to block action against Syria and says any attack would be illegal and only inflame the civil war there.
"I am convinced that (the chemical attack) is nothing more than a provocation by those who want to drag other countries into the Syrian conflict," Russian President Vladimir Putin said on Saturday.
In rebel-held areas, other Syrians were frustrated and disappointed. "God curse everything," said Ahmad Kaddour, an activist in Idlib. "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 group of fighters and activists visited by a Reuters reporter in Aleppo city agreed there would now be no U.S. strike. "This is the same old hesitancy that the United States have tortured us with since the beginning of the revolution," one said. (Additional reporting by Dominique Vidalon in Paris, Ismael Khader in Antakya, Turkey, Tabassum Zakaria, Patricia Zengerle, Douwe Miedema and Paul Eckert in Washington; Denis Dyomkin in Vladivostok, and Khaled Yacoub Oweis in Amman; Writing by David Stamp; Editing by Andrew Roche)