WASHINGTON — Republicans revolted on Saturday over President Trump’s efforts to resuscitate bipartisan stimulus talks with a $1.8 trillion offer to Democrats, balking at what they called an exorbitantly costly plan in the latest sign of steep obstacles to any deal before the election.

Even as Democrats held out for more concessions over funding and provisions from a newly pliant president urgently seeking an agreement before he faces voters next month, it was the deep divisions among Republicans that were standing in the way.

Months of simmering tensions came to a head in a tense phone call Saturday morning between senators and top administration officials, in which nearly half of the Republican conference spent more than an hour lashing into Steven Mnuchin, the Treasury secretary, and Mark Meadows, the White House chief of staff, about the revived negotiations and warning that they could not support much of what was under discussion.

The backlash was so severe that Mr. Meadows at one point told senators that he would relay their concerns to Mr. Trump, but “you all will have to come to my funeral” after he delivered news of such negative reactions.

The stark divisions between most Senate Republicans and what the White House has signaled it was willing to endorse to secure Democratic support further undercut the potential for an agreement before Nov. 3, even as the country’s economic recovery continues to falter and tens of thousands of Americans, businesses and schools struggle to weather the pandemic without federal relief.

Days after abruptly ending negotiations and then reversing course to demand negotiators “go big,” Mr. Trump appears to be faced with two unpalatable choices. Either he is likely to have to concede an inability to wrangle a compromise and deliver critical aid before the election, or defy warnings from his own party in the Senate and pressure Republicans to vote on a proposal that as of now they believe would largely favor Democratic demands. Details of the phone call Saturday morning were described by seven people familiar with the discussion, who all spoke on the condition of anonymity to disclose details of a private conversation.

ImageSteven Mnuchin, the Treasury secretary, continued talks with Ms. Pelosi.
Credit…Anna Moneymaker for The New York Times

Most of the senators who spoke on the call signaled an openness to continuing negotiations. But there was widespread dissatisfaction with both the mounting cost of the administration’s offers and the perception that Mr. Mnuchin, in talks with Speaker Nancy Pelosi, was acquiescing to the Democratic proposal of a $2.2 trillion package as a baseline instead of the two proposals put forward by Senate Republicans this year.

“There’s no appetite right now to spend the White House number or the House number,” Senator Lamar Alexander, Republican of Tennessee, said on the call. Republicans had first offered a $1 trillion proposal in late July, before trying to advance a scaled-down $350 billion proposal that garnered the support of the chamber’s fiscal hawks. (That legislation failed because Democrats blocked it as inadequate.)

Senator Marsha Blackburn of Tennessee, a Republican, warned that accepting a bill with Ms. Pelosi’s support would amount to a “death knell” for the party’s ambitions to retain its majority in the Senate and would “deflate” the Republican base, reflecting longstanding concerns among senators eager to protect their credentials as fiscal hawks and stave off primary challengers in the next election cycle.

Senator John Barrasso, Republican of Wyoming, declared that accepting a Democratic push to expand elements of the Affordable Care Act would be “an enormous betrayal” of Republican voters. Republicans have also voiced concerns that the health care provisions Democrats have pressed for could result in the use of federal funds for abortions, a characterization Democrats dispute.

“I don’t get it,” Senator Rick Scott, Republican of Florida, said of the administration’s efforts to reach a sweeping bipartisan deal with House Democrats, echoing the sentiments of multiple senators.

Ms. Pelosi, for her part, informed Democratic lawmakers that she found elements of Mr. Mnuchin’s proposal to be inadequate, writing in a letter on Saturday that “this proposal amounted to one step forward, two steps back.” After scaling down House Democrats’ original $3.4 trillion proposal to $2.2 trillion, she has been unwilling to accept much less than that.

“When the president talks about wanting a bigger relief package, his proposal appears to mean that he wants more money at his discretion to grant or withhold,” Ms. Pelosi wrote, adding “at this point, we still have disagreement on many priorities.” She ticked off a number of unresolved issues, including what she said was insufficient funding for unemployment benefits, child care, and state and local governments, and “reckless” liability protections that Republicans have insisted are a priority.

The administration’s latest proposal would revive lapsed federal unemployment benefits at $400 a week through mid-January and allow for retroactive payments after Sept. 12, although Democrats have pushed to keep the weekly sum at its original $600 amount. It includes $15 billion for food assistance programs, $25 billion for student loan forgiveness and $60 billion for mortgage and rental assistance.

The offer would also allocate $300 billion to state and local governments and enough funds to increase the $1,200 stimulus payments with an extra $1,000 per child. The addition to stimulus payments, which have bipartisan support, was included as a way to counter Ms. Pelosi’s plan to expand child-related tax credits.

Details of the offer were reported earlier by NBC News and reviewed by The New York Times.

Ms. Pelosi said she was waiting for specific language from the administration about several provisions, including a national strategy for testing and tracing to contain the spread of the virus. It remained unclear whether she and Mr. Mnuchin would speak over the weekend.

Moderate Republicans, particularly those who are facing tough re-election races, are among the few senators who have voiced support for a bipartisan coronavirus deal and expressed few reservations about the price tag. A handful of those senators, on a private call with Senator Mitch McConnell of Kentucky, the majority leader, pushed for action on a bipartisan deal, particularly after Mr. Trump briefly withdrew negotiators from talks and gave Democrats political cover for failure to reach an agreement.

Mr. McConnell has sought to dampen expectations for a deal in recent days, telling reporters in his home state on Friday that “the situation is kind of murky.”

At least one Republican senator, Mike Lee of Utah, also warned that an effort to muscle a spending bill through the Senate could derail efforts to confirm Judge Amy Coney Barrett to the Supreme Court before Nov. 3, while Republicans maintain control of both the White House and the Senate. Confirmation hearings for Judge Barrett to fill the vacancy left by the death of Justice Ruth Bader Ginsburg are set to begin on Monday.

Nicholas Fandos contributed reporting.