Racing in opposition to a Sunday-night deadline to keep away from a authorities shutdown, Congressional leaders labored feverishly on Saturday to resolve an deadlock over a Republican push to curtail the powers of the Federal Reserve that was threatening to derail a compromise $900 billion stimulus plan.

After a monthslong impasse on a brand new pandemic support bundle, Democrats and Republicans had been tantalizingly near finishing an emergency plan to hurry direct funds, unemployment advantages and meals and rental help to tens of millions of People; reduction to companies; and funds for vaccine distribution.

The talks stalled as a C.D.C. panel endorsed a second vaccine, by Moderna, and the nation confronted one other stark reminder of how desperately vaccines are wanted: Friday’s file caseload of over 251,000 new coronavirus instances, practically double the 128,000 individuals who had been vaccinated in the US as of Friday, in accordance with a New York Times database monitoring vaccinations. Officers are warning that hospitals, which now maintain practically 114,000 Covid-19 patients, may quickly be overwhelmed.

Vaccines are additionally being distributed in the UK, the place the raging virus prompted an abrupt reversal on Saturday: Prime Minister Boris Johnson imposed a broad lockdown on London and most of southeast England.

In Washington, with time operating out for a stimulus deal, the 2 sides remained divided over a proposal by Senator Patrick J. Toomey, Republican of Pennsylvania, to make sure the termination of a sequence of pandemic reduction applications created this yr by the Fed and to doubtlessly curtail the central financial institution’s capability to battle monetary crises sooner or later.

“We’re proper inside attain,” Speaker Nancy Pelosi privately informed Home Democrats in a celebration convention name on Saturday. However she mentioned Mr. Toomey’s late-stage calls for to rein within the Fed had been slowing the method.

By Saturday night, Senator Richard J. Durbin of Illinois, the second-ranking Democrat, mentioned the dispute had value negotiators one other day of their efforts to cement a deal.

The rising deal would ship direct funds of $600 to many People and supply enhanced federal jobless funds of $300 per week till early spring. It might additionally present lots of of billions of {dollars} to prop up small companies, colleges and different establishments struggling amid the pandemic.

However Democrats mentioned that Mr. Toomey’s proposal, which has been embraced by Republicans, amounted to an try to undercut President-elect Joseph R. Biden Jr. and his administration’s capability to proceed supporting the nation’s financial restoration.

As drafted, the proposal would stop the Fed and the Treasury Division from re-establishing applications which have helped to maintain credit score flowing to municipal debtors, medium-sized companies and companies throughout the pandemic-related recession. It might additionally bar the creation of comparable applications going ahead.

Lawmakers and aides in each events acknowledged that the Fed provision introduced essentially the most important hurdle to a ultimate settlement, regardless that negotiators had been nonetheless haggling over quite a few excellent technical particulars, together with find out how to present for meals help and the scope of unemployment advantages.

With authorities funding set to lapse Sunday and each chambers hoping to merge the stimulus bundle with a catchall measure to cowl all federal spending for the rest of the fiscal yr, time was dwindling to discover a decision.

With out motion by Congress, two applications designed to increase and improve unemployment advantages are set to run out within the coming days, leaving about 12 million People with out federal help. Plenty of different advantages are set to run out on the finish of the yr.