By Phil Stewart and Khaled Yacoub Oweis

WASHINGTON/AMMAN (Reuters) - Syria accepted a Russian proposal on Tuesday to give up chemical weapons and win a reprieve from U.S. military strikes but serious differences emerged between Russia and the United States that could obstruct a U.N. resolution to seal a deal.

Even as the White House said it was determined to push ahead with a congressional resolution authorizing force, Russian President Vladimir Putin said the weapons plan would only succeed if Washington and its allies rule out military action.

In what amounted to the most explicit, high-level admission by Syria that it has chemical weapons, Foreign Minister Walid al-Moualem said in a statement shown on Russian state television that Damascus was committed to the Russian initiative.

"We want to join the convention on the prohibition of chemical weapons. We are ready to observe our obligations in accordance with that convention, including providing all information about these weapons," Moualem said.

"We are ready to declare the location of the chemical weapons, stop production of the chemical weapons, and show these (production) facilities to representatives of Russia and other United Nations member states," he said.

U.S. Secretary of State John Kerry said Washington believes the proposal must be endorsed by the U.N. Security Council "in order to have the confidence that this has the force it ought to have."

Moscow has previously vetoed three resolutions that would have condemned the Syrian government over the conflict.

The latest proposal "can work only if we hear that the American side and all those who support the United States in this sense reject the use of force," Putin said in televised remarks.

Kerry and U.S. Defense Secretary Chuck Hagel told Congress the threat of military action was critical to forcing Assad to bend on his chemical weapons.

"For this diplomatic option to have a chance of succeeding, the threat of a U.S. military action - the credible, real threat of U.S. military action - must continue," Hagel told the House Armed Services Committee.

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U.S. officials said Kerry would meet Russian Foreign Minister Sergei Lavrov in Geneva on Thursday for further talks.

Amid the whirlwind of diplomatic activity focused on the response to a suspected chemical weapons attack on a Damascus neighborhood on August 21, the civil war resumed in earnest, President Bashar al-Assad's jets again bombing rebel positions in the capital.

UNITED NATIONS

The United States and its allies remain skeptical about the Russian proposal and President Barack Obama sought to keep the pressure on Syria by maintaining his drive for congressional backing for a possible military strike while exploring a diplomatic alternative.

At the United Nations, Britain, France and the United States discussed elements of a draft Security Council resolution that a diplomat from one of the three countries said would include a timeline for Syria to declare the full extent of its poison gas arsenal and to cede control of it to the United Nations.

France said the resolution should be legally binding and state clearly that Syria would face "serious consequences" if it failed to comply with the resolution's demands - diplomatic code for military force. Such language will be resisted by Russia.

The U.N. Security Council initially called a closed door meeting asked for by Russia to discuss its proposal to place Syria's chemical weapons under international control, but the meeting was later canceled at Russia's request.

French officials said their draft resolution was designed to make sure the Russian proposal would have teeth, by allowing military action if Assad is uncooperative.

"It was extremely well played by the Russians, but we didn't want someone else to go to the U.N. with a resolution that was weak. This is on our terms and the principles are established. It puts Russia in a situation where they can't take a step back after putting a step forward," said a French diplomatic source.

Russia, however, made clear it wanted to take the lead.

Lavrov told his French counterpart that Moscow would propose a U.N. draft declaration supporting its initiative to put Syria's chemical weapons under international control, the Russian Foreign Ministry said in a statement.

PUTIN: "NO THREAT OF FORCE"

The United States and France had been poised to launch missile strikes to punish Assad's forces, which they blame for the chemical weapons attack. Syria denies it was responsible and, with the backing of Moscow, blames rebels for staging the attacks to provoke U.S. intervention.

The White House said Obama, British Prime Minister David Cameron and French President Francois Hollande had agreed in a telephone call on their preference for a diplomatic solution, but that they should continue to prepare for "a full range of responses."

Obama asked Congress on Tuesday to delay votes on authorizing military strikes in order to give Russia time to get Syria to surrender its chemical weapons, according to U.S. senators.

"What he (Obama) wants is to check out the seriousness of the Syrian and the Russian willingness to get rid of those chemical weapons in Syria. He wants time to check it out," Senate Armed Services Committee Chairman Carl Levin said.

The White House said Obama, who has called the Russian proposal a potential breakthrough, would still push for a vote in Congress to authorize force when he makes a televised address to Americans later on Tuesday.

But the U.S. congressional vote now appeared more about providing a hypothetical threat to back up diplomacy, rather than to unleash immediate missile strikes. A bipartisan group of senior members of Congress was working on a resolution that would take into account the Russian proposal.

While the prospects of a deal remain uncertain, the proposal could provide a way for Obama to avoid ordering unpopular action. It may make it easier for him to win backing from a skeptical Congress, which could have severely damaged his authority if it withheld support for strikes. Opinion polls show most Americans are opposed to military intervention in Syria, weary after more than a decade of war in Iraq and Afghanistan.

Whether international inspectors can neutralize chemical weapons dumps while war rages in Syria remains open to question.

Western states believe Syria has a vast undeclared chemical arsenal. Sending inspectors to destroy it would be hard even in peace and extraordinarily complicated in the midst of a war.

The two main precedents are ominous: U.N. inspectors dismantled the chemical arsenal of Iraqi leader Saddam Hussein in the 1990s but left enough doubt to provide the basis for a U.S.-led invasion in 2003. Libyan leader Muammar Gaddafi was rehabilitated by the West after agreeing to give up his banned weapons, only to be overthrown with NATO help in 2011.

SYRIAN REBELS DISMAYED

The Syrian war has already killed more than 100,000 people and driven millions from their homes. It threatens to spread violence across the Middle East, with countries endorsing the sectarian divisions that brought civil war to Lebanon and Iraq.

The wavering from the West dealt an unquestionable blow to the Syrian opposition, which had thought it had finally secured military intervention after pleading for two and a half years for help from Western leaders that vocally opposed Assad.

The rebel Syrian National Coalition decried a "political maneuver which will lead to pointless procrastination and will cause more death and destruction to the people of Syria."

Assad's warplanes bombed rebellious districts inside the Damascus city limits on Tuesday for the first time since the poison gas attacks. Rebels said the strikes demonstrated that the government had concluded the West had lost its nerve.

"By sending the planes back, the regime is sending the message that it no longer feels international pressure," activist Wasim al-Ahmad said from Mouadamiya, one of the districts of the capital hit by the chemical attack.

The Russian proposal "is a cheap trick to buy time for the regime to kill more and more people," said Sami, a member of the local opposition coordinating committee in the Damascus suburb of Erbin, also hit by last month's chemical attack.

Troops and pro-Assad militiamen tried to seize the northern district of Barzeh and the eastern suburb of Deir Salman near Damascus airport, working-class Sunni Muslim areas where opposition activists and residents reported street fighting.

Fighter jets bombed Barzeh three times and pro-Assad militia backed by army tank fire made a push into the area. Air raids were also reported on the Western outskirts near Mouadamiya.

But Damascenes in pro-Assad areas were grateful for a reprieve from Western strikes: "Russia is the voice of reason. They know that if a strike went ahead against Syria, then World War Three - even Armageddon - would befall Europe and America," said Salwa, a Shi'ite Muslim in the affluent Malki district.

(Additional reporting by John Irish in Paris, Louis Charbonneau at the United Nations, Thomas Grove and Steve Gutterman in Moscow and Patricia Zengerle, Arshad Mohammed, Richard Cowan, Paul Eckert and Roberta Rampton in Washington; Writing by Peter Graff, David Storey and Claudia Parsons; Editing by Jim Loney)