WASHINGTON, D.C. -- President Obama will address the nation Tuesday night on chemical weapons in Syria, as he and aides pursue a diplomatic proposal at the United Nations that has put military and congressional action on hold.
But as talks began at the United Nations, the U.S. and Russia are at odds over the rules by which Syria might turn over its chemical weapons stockpile to international control, as proposed by Russia.
Obama spoke Tuesday with the leaders of France and the United Kingdom on whether the Russian proposal is workable, said a White House statement.
But Russian President Vladimir Putin told reporters he would only agree to a Syrian chemical weapons hand-off if Obama renounces the use of military force against that country -- even as Obama told senators in a pair of meetings on that the military option must remain open.
Putin said, "It is difficult to make any country -- Syria or any other country in the world -- to unilaterally disarm if there is military action against it under consideration."
Obama and aides said the threat of military force is the major reason Syria has agreed to talk about disposing of its chemical weapons under international supervision.
Still, Obama told senators he wants to see the diplomatic effort play out, rather than pushing for a congressional resolution authorizing military action -- a proposal that faces heavy opposition in any event.
Russia - ally of Syria and opponent of U.S. military strikes - said Monday it would ask Bashar Assad's government to put chemical weapons under international control and have them dismantled; Syria announced Tuesday it would accept Russia's offer, and said it is willing to join a global ban on chemical weapons.
The U.S. Senate, divided over a resolution authorizing military action against Syria, began exploring alternatives in light of the diplomatic moves.
Obama is likely to address diplomatic efforts when he speaks at the White House at 9 p.m. ET Tuesday. He discussed the offer earlier in the day at separate meetings with Senate Republicans and Democrats on Capitol Hill.
The president, who gave six television interviews Monday as a prelude to Tuesday night's speech, expressed skepticism of the Russia/Syria proposal, but said he and his team would study it.
"Let's see if we can come up with language that avoids a strike but accomplishes our key goals to make sure that these chemical weapons are not used," Obama told ABC News.
Defense Secretary Chuck Hagel told a congressional committee Tuesday the administration is "hopeful," but "we must be clear-eyed and ensure it is not a stalling tactic by Syria and its Russian patrons."
Obama discussed the possibility of having the United Nations supervise the collection and dismantling of Syria's chemical weapons in Tuesday phone calls with French President Francois Hollande and British Prime Minister David Cameron.
"The leaders discussed their preference for a diplomatic resolution but stressed the importance of continuing to develop a full range of responses by the international community to the Assad regime's use of chemical weapons near Damascus on August 21," the White House said.
The speech and the Russian proposal come amid intense public and congressional opposition to possible military strikes against Syria in response to that August attack.
The Senate's top Republican, Mitch McConnell of Kentucky, announced he would oppose a resolution authorizing military force, saying "there are just too many unanswered questions about our long-term strategy in Syria."
Meanwhile, a bipartisan group of senators -- some of whom support intervention -- are working on an alternative that would require Syria to allow a United Nations team to remove chemical weapons within a certain time period, perhaps 45 to 60 days. If Syria doesn't comply, Obama would have the authority to launch military strikes.
Assad has denied involvement in the chemical attack, and suggested he may retaliate against any U.S.-led attack.
Obama is struggling to find support in Congress for a resolution authorizing military action in Syria, and votes have been delayed in the wake of the Russian proposal.
During his string of television interviews, Obama acknowledged that he lacks public and congressional support for a military strike.
An NBC News/Wall Street Journal poll released Tuesday finds that nearly 60% of Americans want their member of Congress to oppose the use of military force in Syria. Surveys show a force resolution could go down in both the Democratic-run Senate and the Republican-run House.
In both his speech and briefings with Congress, Obama said he would stress the limited nature of possible military action. He told CBS that "we have a very specific objective, a very narrow military option, and one that will not lead into some large-scale invasion of Syria."
In tentatively embracing the Russian proposal, Obama and aides cited past friction with Russia, and Syria's history of shrouding its chemical weapons program in secrecy.
"I think you have to take it with a grain of salt initially," Obama told NBC News, but added that "we are going to run this to ground."
Russia made its proposal after a seemingly off-handed comment by Secretary of State John Kerry, who said Assad could end the crisis by turning 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 a full and total accounting for that."
But Kerry also said Assad "isn't about to do it, and it can't be done, obviously."
Russia, meanwhile, has consistently blocked U.S. efforts to get the Security Council to authorize a response to Syria over the use of chemical weapons.
Syria has been only one of the friction points between the Obama administration and Russian President Vladimir Putin, including Russia's decision to grant temporary asylum to National Security Agency leaker Edward Snowden.
Last month, Obama canceled a planned summit meeting with Putin.
But Obama told PBS he spoke with Putin on the sidelines of last week's G-20 summit in St. Petersburg, Russia, and he has assigned Kerry to work with the Russians.
"My intention throughout this process has been to ensure that the blatant use of chemical weapons that we saw doesn't happen again," Obama told PBS.
A rising number of lawmakers are expressing opposition to military force.
Rep. Tulsi Gabbard, D-Hawaii, one of two female Iraq War veterans in Congress, said Obama's plan lacks "a clear tactical objective," as well as "an exit plan."
Like many Republicans, Sen. Lamar Alexander of Tennessee said he would oppose authorization because of "too much uncertainty about what comes next."