NEW YORK TIMES, JIM TANKERSLEY, EMILY COCHRANE, NICHOLAS FANDOS

President-elect Joseph R. Biden Jr.’s victory and faster-than-expected breakthroughs on a coronavirus vaccine have shifted the dynamics of stimulus talks in Congress, leading to the first serious bipartisan negotiations in months and empowering rank-and-file lawmakers who have long agitated for a compromise.

With many cities and states reinstating lockdowns and the pace of job creation slowing, congressional lawmakers and Mr. Biden are facing pressure to provide a financial lifeline to the economy until a widespread vaccine forces the virus into submission.

Mr. Biden has used public appearances in recent days to encourage lawmakers to compromise on a quick aid package that he said would only be a “down payment” on what the incoming administration believes is necessary to mitigate the nation’s economic pain in the months ahead. His team has pushed for Democrats to move off their hard-line negotiating stance for a trillion-dollar-plus bill, a stance that had made discussions with Republicans a nonstarter, and to embrace a smaller, bipartisan proposal.

“I think it should be passed,” Mr. Biden said of the $908 billion proposal in a CNN interview broadcast Thursday evening, though he added, “I’m going to have to ask for more help when we get there to get things done.”

Speaker Nancy Pelosi of California and Senator Chuck Schumer of New York, the Democratic leader, announced such a shift on Wednesday, throwing their support behind a bipartisan $908 billion outline as a baseline for restarting negotiations. The plan, which rank-and-file lawmakers are still finalizing, would provide aid through March, offering a new wave of aid to small businesses and the unemployed, helping state and local governments and temporarily shielding businesses from some lawsuits amid the pandemic.

In a sign of momentum, more Republicans also began coalescing around the $908 billion framework as a baseline for restarting negotiations, which had collapsed over disagreements about size and scope.

On Thursday, Ms. Pelosi and Senator Mitch McConnell of Kentucky, the majority leader, spoke for the first time since the November election about another relief package, along with the spending bills needed to avert a government shutdown on Dec. 11. Mr. McConnell later told reporters that he and Ms. Pelosi are “both interested in getting an outcome” on the two issues.

“I’ve never been more hopeful that we’ll get a bill,” said Senator Lindsey Graham, Republican of South Carolina. He told reporters that he supported the bipartisan framework and that he had discussed coronavirus relief with President Trump at the White House on Thursday. But he added a dose of skepticism, given Mr. McConnell’s decision to circulate a blueprint for a smaller relief package.

“I will support what Senator McConnell wants to propose,” Mr. Graham said, “but it doesn’t have any Democratic support. I’m tired of doing show votes here.”

Mr. Biden’s aides, along with Democrats on Capitol Hill, have become alarmed at the possibility that the economy could slip back into recession in the new year, as small businesses shutter and government benefits expire for millions of workers, handing him an even bigger economic challenge.

But Mr. Biden is walking a delicate path in moving toward a possible compromise. He has called publicly for an immediate deal to provide more economic aid, even before he becomes president, and spoken favorably about the bipartisan framework. But he has not directly injected himself into talks between Ms. Pelosi and Mr. McConnell, as some lawmakers and aides stressed that any immediate deal would need Mr. Trump’s signature — not Mr. Biden’s.

“The president-elect has been very clear in stating that something needs to happen, that the American people need relief,” said Representative Abigail Spanberger, Democrat of Virginia and one of several House lawmakers who have worked on compromise legislation in an effort to break through the impasse. When asked if Mr. Biden should be more involved, she said she believed it better for Mr. Biden to play a supporting role while Mr. Trump remained president.

“He will not be president until Jan. 20 — we can’t wait until Jan. 20,” Ms. Spanberger said in an interview. “I don’t think it’s appropriate. He’s not yet the president.”

The question of whether Mr. Trump would support a final compromise remains a wild card. Asked Thursday whether he agreed with Mr. McConnell that pandemic relief was “in sight” and whether he would support “this bill,” Mr. Trump answered affirmatively. “I will, and I think we are getting very close,” Mr. Trump told reporters.

While it was initially unclear which bill Mr. Trump was willing to sign, the White House later clarified that it was the outline of the smaller Republican bill, which Mr. McConnell is backing.

Unlike in the fall, when both Republicans and Democrats had political incentives not to cut a deal, statements by Mr. Biden and his congressional allies in recent days show that lawmakers now see compromise as in their best interests. Depending on the outcome, stimulus plans could become a key issue in the Georgia runoff elections that will decide Senate control in January.

Even with the renewed movement, a deal is far from assured.

Mr. McConnell, who has continuously criticized the Democrats as wanting too expensive a package, acknowledged that it had been “heartening to see a few hopeful signs” this week in negotiations. But Mr. McConnell stopped short of endorsing the compromise plan in remarks on Thursday, admonishing lawmakers to focus on policy provisions where there was substantial agreement and signaling that he would not be quick to move off his targeted proposal.

Even as he declared “compromise is within reach,” he did not explicitly comment on the bipartisan framework. It also remains unclear what top Democrats would insist on in any final bill.

But lawmakers and aides on Capitol Hill acknowledged that a devastating spike in coronavirus cases across the country helped fuel momentum behind the discussions. Even a smaller, more immediate deal would fund an imminent distribution of a vaccine — a prospect that emerged after the election — and leave open the possibility for another relief package under a Biden administration.

“It’s the combination of the logistical costs and difficulties of vaccine distribution and the dramatic spike in cases, hospitalizations and deaths every day,” said Senator Chris Coons, Democrat of Delaware, a longtime close ally of Mr. Biden’s who is involved in the discussions. “It is clear, to everyone I think, that we are in for a very hard winter before the vaccine is broadly available.”

Discussions toward a possible deal began among a loose bipartisan group of senators in mid-November, according to four officials familiar with the behind-the-scenes talks who requested anonymity to describe them. The participants agreed to meet over dinner at the Capitol Hill home of Senator Lisa Murkowski, Republican of Alaska, on Nov. 17, two weeks after Election Day, to see if they could cobble together a plan. Senator Mark Warner, a moderate Democrat from Virginia, picked up the tab for food and drinks from San Lorenzo, a favorite of Washington’s political class for Tuscan food. Fresh off a come-from-behind victory in Maine, Senator Susan Collins, a Republican, agreed to co-host.

They were joined by three more Senate Democrats — Joe Manchin III of West Virginia, Jeanne Shaheen of New Hampshire, and Richard J. Durbin of Illinois, the party’s No. 2 — as well as two more Senate Republicans, Bill Cassidy of Louisiana and Mitt Romney of Utah.

The conversation was productive enough that it quickly spilled into a nearly daily series of Zoom sessions that continued — sometimes for hours at a time — through the Thanksgiving holiday. Pleased at their progress, senators involved dryly dubbed themselves “the dinner group.”

Party leadership was kept informed, but senators did most of the negotiating themselves. Despite his more junior Senate status, Mr. Romney, his party’s 2012 presidential nominee, emerged early on as a driver of the talks with Mr. Warner. He insisted that Republicans could go no higher than roughly $900 billion in new spending — a number that Ms. Collins floated as a possible compromise figure — and that liability protections for employers would have to be included in some form.

The proposal was made final Monday night over a pizza dinner hosted by Mr. Romney in an oversize hearing room. It would providing $300 a week in additional benefits to the unemployed for 18 weeks, after a $600-per-week unemployment benefit lapsed in July. It includes $288 billion for struggling small businesses, restaurants and theaters and $160 billion for strapped cities and states, and most likely will include some liability protections for businesses.

The framework, unveiled Tuesday, quickly received a boost from Mr. Biden. And speaking Thursday on CNN, he noted that he had faith in Ms. Pelosi, Mr. Schumer and Mr. Coons to resolve the impasse, adding that he was “relying on their judgment” in determining “the most basic things that are needed now.”