A number of congressional Democrats erupted in fresh revolt Tuesday in response to a still-forming, bipartisan infrastructure package, arguing the nearly $1 trillion plan is likely to fall short of their ambitions to boost the economy and combat broader challenges including climate change.

The new political rifts emerged over an early compromise prepared by 10 senators from both parties. Their proposal, which has not been released publicly, seeks to break a months-long logjam over stalled public-works spending after talks between President Biden and Senate Republicans broke down earlier this month.

As the architects of the bipartisan Senate plan began pitching its contours to their fellow lawmakers on Tuesday, hoping to build political momentum, multiple Democrats — liberals in particular — lashed out at the approach.

They questioned its price tag, which includes roughly $579 billion in new spending, since it is much smaller than the roughly $2.2 trillion Biden initially put forward as part of his American Jobs Plan. And they raised concerns that Senate negotiators might have traded away too many of their policy priorities in pursuit of Republican support — perhaps jeopardizing Democratic votes in the process.

“The reality is that the American people — Democrats, independents and Republicans — want us to go big, they want us to go bold, and they want us to get it done now because there’s real urgency,” said Rep. Pramila Jayapal (D-Wash.), the leader of the Congressional Progressive Caucus.

The dissent among Democratic ranks had been building behind the scenes for days, with lawmakers conveying publicly and privately to the White House that the administration risked losing support from their own party, particularly if they watered down key climate-change provisions in pursuit of Republican votes. In turn, the administration has quickly convened private calls with key Democrats to assuage their concerns on the issue.

“If they want a bipartisan infrastructure package to have the unified support of the Democratic caucus, those of us who insist on there being serious climate measures at long, long last are going to need specific assurances about how that gets done,” Sen. Sheldon Whitehouse (D-R.I.) said of the administration.

For many Democrats, though, Tuesday appeared to mark a breaking point. Party lawmakers signaled they might not support the still-emerging Senate deal unless they could secure a commitment to move trillions of dollars in additional spending focused on infrastructure and families as part of a second package, potentially at the same time. This is something that Democratic leaders had already pledged to do.

“I don’t think there’s going to be a great fervor for a bipartisan deal unless we’re guaranteed that we’re going to have a big bill,” Sen. Robert P. Casey Jr. (D-Pa.) said Tuesday.

The new Democratic tensions reflected the tall task that Biden — as the party’s leading negotiator — faces in trying to strike a grand bipartisan deal on infrastructure spending. Moving in the direction of the GOP risks alienating some in his own party, a politically unfeasible consequence given that Democrats have only the narrowest majorities in the House and Senate and simply cannot afford defections.

The president, currently in Europe as part of a week-long swing meeting with global leaders, has dispatched Cabinet members and top administration officials to continue shaping his infrastructure initiative on Capitol Hill while he is overseas. White House officials have long indicated that they are content to let the legislative process, no matter how messy, play out, although the administration has also said Biden’s patience is not unlimited.

“This is how negotiations work and our frequent talks with Democrats in both chambers leave us confident,” White House spokesman Andrew Bates said Tuesday. “We continue to work closely with Democrats of all views — as well as Republicans — on the path forward. There are many possible avenues to getting this done, and we are optimistic about our chances.”

In a sign of the precarious politics for congressional Democrats, some Republicans on Tuesday signaled tentative support for the early contours of the Senate’s bipartisan compromise, marking a sharp break with Democrats who criticized it as insufficient.

“I found it to be very interesting … and something I find intriguing that I hope can be worked out,” said Sen. Mike Crapo (R-Idaho), who had taken part of the earlier collapsed talks with the White House.

Asked about the emerging package, Senate Minority Leader Mitch McConnell (R-Ky.) said he is “listening and hopeful that somehow, some way we’ll be able to move forward with an infrastructure bill” that accomplishes two goals — preserving the 2017 tax cuts while paying for the proposal in its entirety.

“I think that’s what the group of 10 are hoping to be able to sell to a large portion of the Senate,” McConnell said in his news conference. “But in the end it will be up to the [Senate] majority leader to decide what to do,” referring to Charles E. Schumer (D-N.Y.).

Democratic leaders, meanwhile, said they plan to proceed on what they describe as two tracks — pursuing a bipartisan compromise while laying the procedural groundwork to forge ahead on their own using a special budgetary move that allows the Senate to adopt legislation using 51 votes instead of 60.

Top party aides said Tuesday that they would explore that process, called reconciliation, not only for the infrastructure package but Biden’s other goals, including the adoption of trillions of dollars in new spending to bolster federal safety net programs and combat climate change. The approach theoretically could allow the parties to reach an agreement on a scaled-back bipartisan infrastructure plan that has only some of what Democrats seek, while still allowing the party to pursue its other priorities as part of a reconciliation package without having to worry about Republicans.

“There are members with very justified views. Whatever you can do, bipartisan, we should try. But alongside that is the view that that won’t be enough," Schumer said at a press conference Tuesday. “So we’re proceeding on both tracks.”

Schumer is set to huddle with Democratic budget leaders to discuss the matter Wednesday.

“The clock is ticking. We’ve got to get moving, and we’ve got to in my view, have reconciliation done by the end of July,” said Sen. Bernie Sanders (I-Vt.), the leader of the budget committee.

The White House, for its part, similarly started to lay the political groundwork for a shift in strategy. With Biden abroad, top administration officials told House Democrats at a private meeting Tuesday that they knows the clock is ticking — and is keeping a close eye on the next seven to 10 days to figure out its strategy.

Some Democrats came away from the gathering and initially interpreted the comments by Steve Ricchetti, one of the president’s top advisers, as setting a deadline for when the White House would cut off talks with Republicans. White House officials later clarified that the comments were meant to reflect that the Biden administration will have a much better sense of where things are headed after that time horizon.

“He said that we are certainly going to know where things stand on infrastructure talks generally in the next week to 10 days, and that we can then take stock overall,” Bates said. “But he did not set a deadline or cutoff.”

An earlier round of talks — between Biden and a top Republican negotiator, Sen. Shelley Moore Capito (W.Va.) — collapsed earlier this month after the two sides could not find common ground over the total price tag for an infrastructure package or the best way to pay for it. Since then, a new group of 10 Senate Democrats and Republicans has emerged with what they hope is a viable alternative, a plan they are set to unveil as soon as Tuesday.

Their proposal is expected to call for about $974 billion in infrastructure spending over five years, which comes to about $1.2 trillion totaled over eight years. About half of it constitutes new spending above what the government might normally spend on infrastructure-related programs and agencies, which is more than GOP lawmakers initially offered — yet less than the $2.2 trillion in new spending included in Biden’s initial American Jobs Plan.

The new bipartisan compromise focuses largely on core infrastructure — such as improvements to roads, bridges, pipes, and Internet connections — and appears to leave out some of the other spending Biden has endorsed targeting schools and low-income families. And it includes no new tax increases, jettisoning the president’s recommendation to raise rates on corporations to finance new public-works projects.

Seeking to build support for the still-forming package, Sen. Mark R. Warner (D-Va.) stressed on Tuesday that “every one of the categories we have are categories President Biden put forward in his plan.”

“Now we don’t take on all the categories President Biden laid out,” he added, “but I think we’ve gotten great response so far.”

Even before its official unveiling, however, some Democrats in Congress had raised alarms with its size and scope, fearing it did not go far enough. The greatest schisms emerged over climate change, since Biden devoted billions of dollars in his American Jobs Package toward combating carbon emissions and investing in new green technology, some of which the GOP opposes. White House officials have mobilized swiftly to tamp down agitation from liberal Democrats who have been increasingly vocal that robust climate provisions will be excised from any infrastructure package that Biden signs into law.

Shortly after progressives began firing off tweets last week, raising alarms that climate priorities will be neglected, White House officials hastily assembled a video call with a roughly a half-dozen Democratic senators on Thursday to assuage their concerns, according to multiple people familiar with the meeting.

On the call, National Economic Council director Brian Deese and Gina McCarthy, the White House’s national climate adviser, listened as the Democratic senators stressed to them that this year represented a once-in-a-generation chance to enact significant climate legislation. Senators concluded the call satisfied that the administration heard their concerns.

“I don’t think they were unaware of the possibility of grouchy progressives, but I think they were unaware of the extent of it and figured that was a problem for a later day,” said a participant on the call, speaking on the condition of anonymity.

The White House did not comment on the meeting.

But Democrats revived their criticisms on Tuesday. In the Senate, Democratic Sens. Edward J. Markey (D-Mass.) and Jeff Merkley (D-Ore.) held a news conference Tuesday afternoon to lay down a marker of their own, stressing any eventual compromise must include significant provisions to address climate change.

“It’s time for us to put on that classic song by Fleetwood Mac — it’s time for us to go our own way,” Markey said Tuesday. “This is as clear as day. No climate, no deal. ”

Others rose anew in defense of Biden’s initial proposal, including his plan to invest billions of dollars in new electric vehicle charging stations. Rep. Debbie Dingell (D-Mich.) emerged from House Democrats’ meeting with top White House officials on Tuesday stressing she would not vote for a package that omitted the funding.

Reflecting on the talks, she praised the president for trying to “bring people together and pass an infrastructure bill.”

“But at some point,” Dingell said, “you got to fish or cut bait.”

Jeff Stein contributed to this report.