Obama will meet top Republican and Democratic Party chieftains at the White House at 1900 GMT -- and demand that Congress raises America's borrowing authority before Thursday deadline.
The government itself meanwhile hit the two week mark of a partial shutdown which has damaged US prestige and will soon begin to have an increasingly onerous impact on economic output.
Despite massive stakes for Washington and the world, there was still no clear path to resolving potentially the most serious impasse yet between Obama and his Republican foes on Capitol Hill.
Obama will meet Republicans House Speaker John Boehner and Senate minority boss Mitch McConnell and Senate Democratic leader Harry Reid and the party's House minority leader Nancy Pelosi.
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"The president will also reiterate our principles to the leaders: we will not pay a ransom for Congress reopening the government and raising the debt limit," the White House official said.
"The president continues to urge Congress to pass a bill that raises the debt ceiling and lends the certainty our businesses and the economy needs."
"This environment is different than any that I have seen around an arrangement like this," Republican Senator Bob Corker told NBC's "Today Show."
The uncertainty was mirrored on Wall Street, where increasing concern over the fiscal showdown pulled the Dow Jones Industrial Average down 57 points or 0.3 per cent in mid morning trade.
Yet there was little panic, but a sense that the wrangle over raising the debt ceiling would be eventually be solved at the eleventh hour -- like many other recent political imbroglios.
"I'm optimistic about the prospect for a positive conclusion," Reid said on Sunday.
The most likely scenario appears to be some kind of short-term deal to raise the debt ceiling for a number of weeks, and possibly to return thousands of federal furloughed workers to their jobs.
Republican Senator Roger Wicker told MSNBC he was hopeful of seeing "something meaningful by the end of the day.