By Roberta Rampton and Thomas Ferraro
WASHINGTON (Reuters) - President Barack Obama said on Monday the United States would explore Russia's potential "breakthrough" plan to put Syria's chemical weapons under international control but would keep the pressure on Damascus by asking Congress to authorize U.S. military strikes.
In a series of television interviews designed to persuade Congress and the American public of the need for intervention, Obama said he would pause any military action if Syria would relinquish control of its chemical weapons arsenal.
Congress sought to buy more time to explore Russia's offer. Democratic Senate leader Harry Reid pushed back a Wednesday test vote on authorizing military strikes to possibly later in the week.
"I don't think we need to see how fast we can do this. We have to see how well we can do this," Reid told his colleagues.
The surprise diplomatic course opened up after U.S. Secretary of State John Kerry made an unscripted comment earlier on Monday. Kerry suggested in London, in response to a reporter's question, that Syrian President Bashar al-Assad could avoid a military strike by surrendering his chemical arsenal.
Russia pounced on the comment, and Syria also said it was open to a proposal to put the weapons under international control.
Obama said he prefers a diplomatic solution in Syria, but is still skeptical.
"This could potentially be a significant breakthrough," Obama told NBC News in an interview. "But we have to be skeptical because this is not how we've seen them operate over the last couple of years."
Administration officials also said the proposal would not derail efforts to get congressional authorization for strikes, saying it was the threat of strikes that motivated Russia's offer.
Obama faces an uphill struggle to win approval on military intervention from Congress, where a majority of lawmakers are still undecided on whether to use military force to punish Syria for an August 21 chemical weapons attack on civilians.
'WOULDN'T SAY I'M CONFIDENT'
"I wouldn't say I'm confident" of winning approval, Obama told NBC, but he plans an intensified lobbying blitz for support over the next few days.
In addition to the television interviews, Obama was due to visit the Capitol on Tuesday to make his case to lawmakers from both parties before making a televised address to the nation from the White House in the evening.
Some lawmakers reacted positively to the Russian plan. Republicans John McCain and Lindsey Graham, leading supporters of the strikes, said the Russian proposal should make it easier to win support in Congress.
Senator Dianne Feinstein, Democratic chairwoman of the Senate Intelligence Committee, said Russia could be "most effective" in encouraging Assad to place his chemical arsenal under U.N. control.
"I do think that the Russians are serious. I met with the Russian ambassador earlier today and believe that they are serious in putting this together and that it is a plan that could solve the problem," she said.
Former Secretary of State Hillary Clinton, a potential presidential candidate in 2016, waded into the debate, endorsing Obama's drive for Congress to approve military action and saying Syria's surrender of chemical weapons would be an "important step."
Hundreds of House members attended a Syria briefing late on Monday by Kerry and Defense Secretary Chuck Hagel. Many members expressed interest in the Russia proposal, along with a dose of skepticism.
"We should very quickly and clearly find out if this thing is real," said Representative Eliot Engel, the top Democrat on the House Foreign Affairs Committee. "I'm dubious, because Russia's been a very bad player on this, blocking everything we've tried to do in the United Nations."
The Russian proposal could make it harder for the administration to build political momentum for military strikes by giving an excuse to some lawmakers to say they prefer to let the diplomatic process play out.
'THROWS A WRENCH'
"It basically throws a bit of a wrench into the administration's approach," said Robert Danin, a Middle East expert at the Council on Foreign Relations. "But it may be a welcome wrench."
Some members of Congress said Obama has lost support for a strike over the last week and polls indicated Americans, weary after wars in Afghanistan and Iraq, strongly opposed military action.
A Reuters/Ipsos poll released on Monday showed opposition to a U.S. military strike was increasing. The poll, taken Thursday through Monday, indicated 63 percent of Americans oppose intervention, up from 53 percent in a survey ending August 30.
Mike Rogers, Republican chairman of the House Intelligence Committee and a supporter of strikes, said on Monday that Obama had "fumbled" the message on Syria and faced a critical moment.
"Mr. President, lay out the case. It's an important case for the future national security of this country. You're right on your decision, now show Americans why you believe it's right," Rogers said on MSNBC. "And when he does that, I think we're going to get votes."
Assad, in an interview with CBS television, denied there was any evidence linking his government to the attack and warned that if there were strikes against Syria, the United States should expect reprisals.
Susan Rice, making her first major speech since taking over as Obama's national security adviser, said the United States cannot allow countries such as North Korea and Iran to think Washington would not react to a chemical weapons attack.
"We cannot allow terrorists bent on destruction, or a nuclear North Korea, or an aspiring nuclear Iran, to believe for one minute that we are shying away from our determination to back up our longstanding warnings," she said at the New America Foundation think tank.
(Additional reporting by Arshad Mohammed, Susan Heavey, Caren Bohan, Richard Cowan, Patricia Zengerle and Deborah Charles; Writing by John Whitesides; Editing by Karey Van Hall, David Storey and Jim Loney)