(Adds U.S. poll, Kerry comments to Lavrov)
* Russia takes up Kerry remark, proposes chemical arms deal
* Syria "welcomes" Russian proposal, echoed by U.N. chief
* U.S. "skeptical" as Obama seeks lawmakers' approval to strike
* Rebels in Syria denounce Russian plan as delaying tactic
By Stephen Kalin and Arshad Mohammed
BEIRUT/LONDON, Sept 9 (Reuters) - As President Barack Obama struggled to rally Congress and the American people behind military action in Syria, Russia seized on a remark by his secretary of state on Monday to say Damascus should save itself by handing over its chemical weapons.
John Kerry was quick to dismiss as hypothetical his own comment that Syrian President Bashar al-Assad could avert U.S. strikes by surrendering his chemical arsenal to international control. But Assad's ally Russia quickly turned it into a firm proposal that was "welcomed" by Damascus and echoed by U.N. chief Ban Ki-moon.
Rebels fighting Assad's forces on the ground, where hundreds are being killed by conventional bullets and explosives every week, dismissed any such weapons transfer as impossible to police and a decoy to frustrate U.S. plans to attack.
The White House said it was "seriously skeptical" but would take a "hard look" at the proposal.
Kerry later called Lavrov to tell him that while his remarks had been rhetorical and the United States was not going to "play games," if there was a serious proposal, then Washington would take a look at it, a senior U.S. official said.
With President Obama preparing to make his case in television interviews later on Monday to Americans wary of involvement in another distant war, the armaments proposal could complicate his task - or give the president an alternative to military action.
The outcome of votes in Congress remains hard to predict.
Obama has argued that Assad, fighting to continue his family's four-decade rule in a civil war well into its third year, must be punished for what Washington says was a poison gas attack on rebel areas that killed over 1,400 people on Aug. 21.
The president surprised friends and foes by turning to Congress for approval, delaying any U.S. response.
Asked by a reporter during a visit to London whether there was anything Assad's government could do or offer to stop a U.S. military strike, Secretary of State Kerry answered:
"Sure. He could turn over every single bit of his chemical weapons to the international community in the next week - turn it over, all of it without delay and allow the full and total accounting. But he isn't about to do it and it can't be done."
The State Department later said Kerry had been making a rhetorical argument about the impossibility of Assad turning over chemical weapons, which Assad denies his forces used.
Less than five hours later, Russian Foreign Minister Sergei Lavrov said he had put what sounded like Kerry's proposal to his visiting Syrian counterpart during talks in Moscow. Walid al-Moualem said Damascus welcomed the Russian initiative - while not spelling out whether Syria would, or even could, comply.
Russian President Vladimir Putin has blocked U.N. action against Assad and says Obama would be guilty of unlawful aggression if he launches an attack without U.N. approval.
Lavrov said: "If the establishment of international control over chemical weapons ... makes it possible to avoid strikes, then we will immediately get to work with Damascus."
Lavrov said Russia was also urging Syria to eventually destroy the weapons and become a full member of the Organisation for the Prohibition of Chemical Weapons (OPCW).
Shortly afterward, United Nations Secretary General Ban took up the same theme, saying that he might ask the Security Council to end its "embarrassing paralysis" over Syria and agree to act.
Asked about Lavrov's proposal, Ban said: "I'm considering urging the Security Council to demand the immediate transfer of Syria's chemical weapons and chemical precursor stocks to places inside Syria where they can be safely stored and destroyed."
Ban has said that any action that lacks the approval of the world security body could worsen the situation in Syria.
U.N. chemical weapons inspectors were in Damascus at the time of the mass poisoning, which Assad and Putin have blamed on rebel forces. Ban said that if the evidence they were able to gather - after lengthy bargaining over their movements with Syrian officials - proved the use of toxins, the world must act.
Syria, which has never signed a global treaty banning the storage of chemical weapons, is believed to have large stocks of sarin, mustard gas and VX nerve agents - the actual use of which is banned by a 1925 treaty to which Damascus is a signatory.
White House officials made clear their skepticism of the feasibility of the Russian proposal. Syria is a battleground where access for foreign experts would be dangerous. And it would be very hard to verify whether all sites had been sealed.
Years of cat-and-mouse maneuvering between U.N. weapons inspectors and Saddam Hussein in neighbouring Iraq show how difficult it might be to enforce any arms control orders on a timetable that would satisfy Washington in the midst of a war.
In his conversation with Lavrov, Kerry voiced "serious skepticism" and said that such a proposal would not be a reason to slow White House efforts to secure congressional backing for the use of force, according to the U.S. official.
Qassim Saadeddine, a rebel commander in northern Syria and a spokesman for the Supreme Military Council of Assad's opponents, said: "It is a trap and deceitful maneuver by the Damascus regime and will do nothing to help the situation.
"They have tons of weapons hidden that would be nearly impossible for international inspectors to find."
Putin, however, would see major diplomatic advantages to any plan that bolstered Russia's role in brokering international settlements and thwarted strikes in which Obama may have French military support.
The Russian proposal won a cautious welcome in public from both the British and French governments, Obama's main European allies in the crisis.
In Washington, U.S. Deputy National Security Adviser Tony Blinken said the United States would take "a hard look" at the idea but that Congress should still approve a military action.
"It's important to note that this proposal comes in the context of the threat of U.S. action and the pressure that the president is exerting," he said. "So it's even more important that we don't take the pressure off and that Congress give the president the authority he's requested."
Kerry said he was confident of the evidence that the United States and its allies had presented to support their case that Assad's forces used poison gas, though he said he understood scepticism lingering from accusations against Saddam that led to the U.S. invasion of Iraq in 2003 and later proved to be false.
Kerry, a former lawyer, said he had successfully prosecuted people with less evidence and warned that doing nothing was worse than doing something, saying inaction would come back to haunt the United States and its allies: "If you want to send Iran and Hezbollah and Assad a congratulatory message: 'You guys can do what you want,' you'd say: 'Don't do anything.'
"We believe that is dangerous and we will face this down the road in some more significant way if we're not prepared to take ... a stand now," Kerry said.
Obama planned six television interviews later on Monday and was to speak to lawmakers at the Capitol on Tuesday before a televised address from the White House in the evening.
The Senate will hold a test vote on Wednesday.
A survey by the newspaper USA Today on Monday found majorities of both houses remained uncommitted - reflecting broad and growing public opposition to military action.
A Reuters/Ipsos poll on Monday showed Americans' opposition to a U.S. military strike against Syria was increasing. The poll, conducted Sept. 5 to 9, indicated that 63 percent of Americans opposed intervening in Syria, up from 53 percent in a survey that ended Aug. 30. About 16 percent of Americans surveyed said the United States should get involved - down from 20 percent on Aug. 30.
Tapping into concerns in the West about the role of Islamist militants in the rebel forces, Syrian Foreign Minister Moualem said: "We are asking ourselves how Obama can ... support those who in their time blew up the World Trade Center in New York."
Assad himself warned of reprisals - if he were attacked Americans could "expect every action", he told CBS television.
Repercussions "may take different forms" and could include "instability and the spread of terrorism all over the region that will influence the West directly".
Brent crude oil futures sank more than 2 percent on Monday, as the prospect of a wider war in the Middle East appeared to recede into the future: "This has thrown some sand into the wheels of military preparation in the U.S.," said Michael Lynch of Strategic Energy & Economic Research.
"At the very least, it means the debate is going to be stalled while we wait and see if it works out."
There is a chance now that a U.S.-led military strike could be "put on hold and possibly deterred altogether".
Inside Syria, government forces launched an offensive to wrest back control of an historic Christian town north of Damascus on Monday, activists said. In the past six days, the town of Maaloula has already changed hands three times between Assad's forces and rebels, some of whom are linked to al Qaeda. (Writing by Alastair Macdonald and Claudia Parsons; Editing by Andrew Heavens and David Storey)