Democratic US House Speaker Nancy Pelosi withdrew a promised vote on a $1.2 trillion infrastructure bill late Thursday after failing to win enough support from her own lawmakers, in a stark illustration of the deep internal divisions threatening President Joe Biden's agenda.

The California congresswoman had promised to put up the legislation in the lower chamber after it advanced from the Senate with cross-party support, with moderates keen to notch an easy victory for Biden on what would be one of the largest spending packages in history.

But progressives insisted they would sink the proposals after getting no clear sign from the centrist faction that they would commit to an even broader $3.5 trillion social spending package Biden is touting as the cornerstone of his plan to transform the US economy.

The threat left Pelosi with a dilemma: bring the infrastructure bill to the floor, where it has very little Republican support and would likely be sunk by Democratic liberals, or risk the ire of moderates by announcing a delay.

Pelosi didn't comment immediately, but the White House vowed to bring the warring groups back to the table on Biden's two-pronged strategy first thing on Friday.

"A great deal of progress has been made this week, and we are closer to an agreement than ever," Biden's press secretary Jen Psaki said in a statement.

"But we are not there yet, and so, we will need some additional time to finish the work, starting tomorrow morning first thing."

The prospect of the infrastructure bill being signed into law appeared to be out of reach throughout a day of intense negotiations in Congress and the White House, with no agreement on the contents or proposed ticket price for the giant social welfare bill, known as "Build Back Better."

A group of Republicans who backed the infrastructure deal in the Senate, including former presidential candidate Mitt Romney, released a statement saying they were "disappointed" with the setback but hopeful the bill would eventually succeed.

A long day in Washington had started on a brighter note with Congress sending a stopgap bill with support from both parties for Biden's signature to avert a damaging government shutdown at midnight -- when the fiscal year ends.

It was a rare show of cross-party unity that only threw into sharper relief the Democratic leadership's struggle to overcome fierce infighting among its rank-and-file.

"There's so much more to do," the president said in a statement after signing the measure into law.

"But the passage of this bill reminds us that bipartisan work is possible and it gives us time to pass longer-term funding to keep our government running and delivering for the American people."

Despite some progress behind the scenes, Democratic progressives and moderates remain entrenched in a public war of words over the massive twin spending programs, as Republicans enjoy the disarray from the sidelines with one eye on next year's midterm elections.

The progressives don't trust that centrists, who object to the size and scope of the larger Build Back Better package, will honor an agreement to pass the legislation once infrastructure is across the line.

West Virginia Senator Joe Manchin inflamed tensions Wednesday with a statement arguing that trillions of dollars in extra spending was "fiscal insanity," solidifying opposition to the smaller infrastructure bill.

He told reporters Thursday that he was unwilling to go above $1.5 trillion.

Pelosi -- who maintains that she won't put out any bill that doesn't have the support -- had initially planned to forge ahead on the infrastructure vote but the necessary backing never looked like it was materializing.

That eventually forced her hand and she now faces the option of trying again on Friday or putting the infrastructure package on ice and returning to it when the plan for the larger proposal is more fully formed.

The late developments were not a fatal blow to Biden's agenda, although the delay will be a frustration to White House aides who risk losing momentum after spending the week marshalling lawmakers.

A delay would also see the way clear for tempers to cool while Congress focuses on other enormous challenges, such as raising the debt limit.

The US is nerve-janglingly close to defaulting on its $28 trillion debt, with 19 days to go until the Treasury Department exhausts its ability to obtain new loans.

No one in the leadership of either party has spelled out a clear way to avoid the crisis, which would tank the US economy and roil world markets.

Republicans are demanding that Democrats -- whom they regard as profligate over-spenders -- carry the political burden of running up the debt on their own as they control Congress and the White House.

But Democrats are against using the arcane budget process known as "reconciliation" to pass the extension without Republican support. It would take three to four weeks, they argue, making it a non-starter.

The House passed a debt limit hike Wednesday on a party-line vote, but it has been rejected by Republican Senate leader Mitch McConnell.