US officials are optimistic they will pass a $US900 billion ($A1.2 trillion) coronavirus aid package after senators struck a late-night compromise to clear one of the final hurdles, a dispute over Federal Reserve pandemic lending authorities.

Congressional leaders plan to attach the coronavirus aid package, which includes $US600 ($A787) direct payments to individuals and a $US300 ($A393) per week unemployment compensation supplement, to a $US1.4 ($A1.8) trillion spending bill funding government programs through to September 2021.

Sources briefed on the matter told Reuters on Sunday the deal was expected to grant US airlines $US15 billion ($A20 billion) in payroll assistance that will allow them to return more than 32,000 workers to their payrolls by March 31.

The deal would also include $US1 billion ($A1.3 billion) for rail service Amtrak, $US14 billion ($A18 billion) for public transit systems and $US10 billion ($A13 billion) for state highways, one of the sources said.

The senators face a funding deadline of midnight on Sunday local time, risking a government shutdown without action.

Republican Senator Pat Toomey had insisted on language that would guarantee that the central bank could not revive emergency lending programs after December 31, when they expire under the CARES Act COVID-19 relief legislation passed in March.

Republicans had said the programs are an unnecessary government interference in private business that politicises the Federal Reserve, while Democrats accused their rivals of trying to tie the Fed’s hands in order to limit President-elect Joe Biden’s options for boosting the flagging economy after he takes office on January 20.

“I do have optimism that it’ll pass,” House Republican leader Kevin McCarthy said in an interview on Fox News.

“I am very hopeful that we get this done today.”

The Senate adjourned a rare Saturday session with a call from Republican leader Mitch McConnell to avoid last-minute disagreements that could delay new funding.

“I believe there is going to be a deal. There are always sticking points, but the big one was resolved last night,” Republican Senator Mitt Romney told CNN on Sunday.

“They’re working out some additional points. But I think it’s going to get done. It’ll get done before Christmas.”

In the 11 months since the first cases were documented in the United States, COVID-19 has killed more than 316,000 Americans, by far the most in the world, and put millions out of work, with unemployment rising.

President Donald Trump, whose administration has largely left negotiations up to congressional leaders, complained early on Sunday morning that a deal had not been reached.

“Why isn’t Congress giving our people a Stimulus Bill? It wasn’t their fault, it was the fault of China,” Trump said on Twitter. “GET IT DONE, and give them more money in direct payments.”