President Obama's "Plan A" for a military strike on Syria could be in danger just one day before he makes his case to the American people as Russia, the U.N. and some in Congress push for a newly emerging "Plan B."

Gaining traction is a push to compel the Assad regime to turn over its chemical weapons.

The idea caught fire unexpectedly on Monday after Secretary of State John Kerry made an off-hand comment that Syria could resolve the stand-off by relinquishing its chemical weapons within a week. Kerry claimed that Assad "isn't about to do it" -- and an aide suggested the secretary was not being serious.

But within hours, Russian Foreign Minister Sergey Lavrov said Moscow would push Syria to place its chemical weapons under international control.

Officials with the State Department and the White House have since said they'll take a "hard look" at the Russians' proposal.

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"We would welcome Assad giving up his chemical weapons. ... That would be terrific," White House Deputy National Security Adviser Tony Blinken said, while stressing that Congress should still vote to authorize the use of force in order to keep the pressure on Syria.

U.N. Secretary-General Ban Ki-moon and British Prime Minister David Cameron also reportedly indicated support for the plan to have Syria turn over chemical weapons to international control. And a pair of U.S. senators is already pushing an alternative resolution in Congress that would achieve similar goals.

Sens. Joe Manchin, D-W.Va., and Heidi Heitkamp, D-N.D, who are opposed to a strike on Syria at this time, are pushing a resolution that would give Syria 45 days to join the international convention against chemical weapons and take "concrete steps" to comply with it.

In a written statement, Heitkamp said this would have Bashar Assad "begin the process of turning over its chemical weapons."

"If, after 45 days, the Assad regime mistakes our deliberate and careful democratic process for lack of will and immunity, it does so at its own peril," she said.

Manchin and Heitkamp have been promised a vote on their proposal, Fox News is told.

It's unclear whether the Obama administration, which is pushing a military strike in response to an Aug. 21 chemical weapons attack blamed on the Assad regime, will seriously consider these offers.

State Department spokeswoman Jen Psaki seemed to walk back Kerry's original remark, clarifying that Kerry "was making a rhetorical argument about the impossibility and unlikelihood of Assad turning over chemical weapons he has denied he used."

She added: "His point was that this brutal dictator with a history of playing fast and loose with the facts cannot be trusted to turn over chemical weapons otherwise he would have done so long ago."

But the State Department said later in the day that it would take a "hard look" at the proposal.

Lavrov said he has already handed over the proposal and expects a "quick, and hopefully, positive answer."

"We are calling on the Syrian leadership to not only agree on placing chemical weapons storage sites under international control, but also on its subsequent destruction and fully joining the treaty on prohibition of chemical weapons," he said.

Syria's foreign minister said the country welcomes the Russian proposal.

The alternative plan could offer Obama, who is planning a national address on Tuesday, a lifeline as he prepares for a tough set of votes on Capitol Hill. The Senate could hold a key test vote as early as Wednesday. However, with the defection of Heitkamp and many others, it will be a tough climb to corral the 60 votes that are likely necessary to advance the use-of-force resolution. The House is an even tougher sell.

Senate Democratic Leader Harry Reid was expected to formally tee up the test vote on Monday.

Lavrov's statement followed media reports alleging that Russian President Vladimir Putin, who discussed Syria with Obama during the group of 20 summit in St. Petersburg last week, sought to negotiate a deal that would have Assad hand over control of chemical weapons.

Speaking earlier in the day, Lavrov denied that Russia was trying to sponsor any deal "behind the back of the Syrian people."

The Associated Press contributed to this report.