WASHINGTON — President Biden mounted an urgent effort Wednesday to rescue his first-term agenda from potential collapse, attempting to broker a political truce among Democrats that would foster swift passage of roughly $4 trillion in new economic spending initiatives.

Over a series of three meetings, spanning five hours, Biden sought to confront the schisms that have separated his party for months – a division between spending-wary moderates and ambitious liberals that has cast doubt on Democrats’ ability to deliver on the promises they made during the 2020 election.

Democrats returning to the Capitol after the sessions praised Biden’s involvement and pledged to work together in the weeks to come, as they seek to pass a roughly $1 trillion bill to improve the nation’s infrastructure and another roughly $3.5 trillion measure that includes major changes to federal health care, education, climate and tax laws.

“He reminded everybody that politics is the art of the possible and in order to enact the Biden agenda, everybody is going to have to give a little,” Sen. Brian Schatz, D-Hawaii, said after the meetings. “He never made this explicit, but implicitly reminded us that we have to quit squabbling. I thought it was important in terms of tone-setting.”

But party lawmakers appeared no closer to resolving their fight over the size, scope and timing of those two tranches of proposed spending, creating renewed tension five days before the House is set to cast its first vote on one of the Democrats’ core proposals.

The immediate political standoff stems from a promise by House Speaker Nancy Pelosi, D-Calif., to hold a vote on a bipartisan infrastructure bill to improve the nation’s roads, highways, pipes, ports and Internet connections. The package is embraced by Democratic centrists, who secured a commitment from party leaders for the House to consider the measure by Monday.

The party’s liberals, however, are equally passionate about the separate $3.5 trillion tax-and-spending bill, which includes a slew of new programs to help low-income Americans. Some centrists reject that price tag as exorbitant – but liberals insist they won’t support the infrastructure bill without it, leaving Democrats worried that both bills could ultimately fail.

Hoping to stave off an embarrassing defeat on the House floor next week, Biden on Wednesday began his burst of congressional outreach by huddling with moderates including Sens. Joe Manchin III, D-W.Va., and Kyrsten Sinema, D-Ariz. The two lawmakers are among a vocal group of centrists who have called for scaling down the $3.5 trillion package, to the frustration of liberals.

Privately, the centrist lawmakers on Wednesday discussed with Biden an alternative tax-and-spending plan in the range of about $2 trillion, according to a person familiar with the matter who requested anonymity to describe the private conversation. But no agreement was reached on a final figure that moderates would support as a bloc, another person said, despite Biden’s repeated urging that the lawmakers come to an agreement.

Exiting their meeting, moderates including Manchin said Democrats still need “a lot more time” to complete that bill. Others, including Rep. Josh Gottheimer, D-N.J., said they believe the infrastructure vote is on track to proceed Monday as planned.

Liberal-leaning lawmakers, meanwhile, emerged from their own White House gathering reiterating their threat to oppose the infrastructure bill absent an agreement on the social spending package. Even as she praised the discussion with Biden, Rep. Pramila Jayapal, D-Wash., leader of the Congressional Progressive Caucus, reiterated that perhaps half the roughly 100-member bloc could vote against the infrastructure measure Monday if the shape of the $3.5 trillion tax-and-spending bill is not finalized by then.

“This is the president’s agenda, this is the Democratic agenda, and this is what we promised voters when they delivered us the House, the Senate, and the White House,” Jayapal said in a statement.

Senate Finance Committee Chairman Ron Wyden, D-Ore., who attended the liberals’ meeting, said the progressives made the case to Biden that the Monday deadline is largely arbitrary and could be moved. Biden was noncommittal, Wyden recounted, saying only that he understood their argument and would need to speak to Pelosi and Schumer.

“I’ve been hearing members say, ‘What’s so magical about Sept. 27? We don’t even have scores, and we still have differences of opinion and the like,’ ” Wyden said. “And the president heard us out.” Wyden was referring to the “scoring” of a bill, the official calculation of its cost by the Congressional Budget Office.

That raised the prospect that dozens of liberal Democratic defections could sink the infrastructure bill next week unless House Republicans cross the aisle to support it. House GOP leaders earlier Wednesday said they would urge members to oppose the proposal, however.

The White House issued a brief summary of the meetings, saying that “progress was made” and that “there is more work ahead in the coming days, and [Biden] and his team will have follow-up meetings, starting tomorrow, to continue to advance the process of passing these critical bills.”

The bickering reflected months of tension within a party that controls Congress by the slightest of margins. And it came at a time when Democrats are facing a raft of additional challenges, including the potential for a government shutdown next week and a potentially catastrophic breach of the government’s debt ceiling in October.

“When you’ve got 50 votes and none to lose, and you’ve got three to spare in the House, there’s a lot of give and take – that’s just the way it is,” said Sen. Bernie Sanders, I-Vt., a chief architect of the $3.5 trillion plan.

Democrats from all factions view the stakes as unusually high, since analysts expect Democrats to lose at least the House in 2022, making the current window potentially their last chance for years to enact a broad agenda.

That is the maelstrom Biden stepped into Wednesday.

“We are in a pivotal period of our negotiations and discussions” that requires Biden’s “deeper engagement,” White House press secretary Jen Psaki told reporters before Biden sat down with Democrats. “This is a messy, sausage-making process. . . . He’s rolling up the sleeves, he’s welcoming them to the Oval Office, he’ll have some covid-safe snacks.”

A key unresolved question is what the broader social spending bill favored by the liberals will ultimately look like. The current $3.5 trillion package includes such longtime goals as an expansion of Medicare to include hearing, vision and dental care; universal prekindergarten; free community college tuition; and a sweeping climate plan.

Centrists say they cannot accept a package of that size – and Manchin in particular has suggested the bill will have to shrink to something closer to $1.5 trillion to win his support. During the private discussion Wednesday, some moderate Democrats suggested that lawmakers should agree on a combination of revenue-raisers – primarily tax increases – that could pass both the House and Senate, and let that figure become the new total price tag, according to a person briefed on the meeting who also spoke on the condition of anonymity. Liberals have dismissed such ideas.

Democratic leaders have stressed to their members in recent days that they must stick together to deliver Biden’s agenda or risk having it collapse, with potentially devastating political consequences for the party. Some have warned against the potentially terrible optics if their own party torpedoes the Biden-backed infrastructure proposal Monday in full public view on the House floor.

“There will not be a positive reaction to help coalesce our caucus if the infrastructure bill goes down,” House Majority Leader Steny H. Hoyer (D-Md.) said this week. “I don’t agree with the judgment of those who think that somehow it will compel the moderate wing of the caucus to be more supportive. I think the moderate wing is supportive.”

Liberal Democrats in the Senate, however, offered support to their House counterparts Wednesday, as 11 senators led by Sanders called on the House to delay Monday’s infrastructure vote. The package passed the Senate on a bipartisan basis earlier this year.

“We voted for the bipartisan infrastructure bill with the clear commitment that the two pieces of the package would move together along a dual track,” the lawmakers wrote. “Abandoning the $3.5 trillion Build Back Better Act and passing the infrastructure bill first would be in violation of that agreement.”