US House Speaker Nancy Pelosi speaks with reporters during her weekly press conference at the US Capitol March 26, 2020, in Washington, DC.

The U.S. Congress on Monday inched toward a $450 billion deal to help small businesses and hospitals hurt by the coronavirus pandemic, with House Speaker Nancy Pelosi saying negotiators had come to terms on the 'principles' of the package as the Senate set a Tuesday session for a potential vote.

Republicans and Democrats have been battling for more than a week over what to include in the fourth round of financial stimulus intended to ease the heavy economic toll of a pandemic that has killed more than 42,000 Americans.

In an interview with CNN, Pelosi said Republican and Democratic negotiators were still in talks, adding: "I feel very optimistic and hopeful that we'll come to a conclusion tonight."

"We have I believe come to terms on the principles of the legislation, which is a good thing ... now we're down to the fine print," Pelosi said.

The two sides had sought to finish the package earlier on Monday, but failed amid continued disagreements over, among other things, a coronavirus testing strategy.

"However, since this is so urgent, I've asked that the Senate meet again ... and the Democratic leader has agreed to my request," Majority Leader Mitch McConnell said on the Senate floor.

The 78-year-old Republican then left the chamber, putting on a mask to speak briefly with reporters in the hallway.

Pelosi had told fellow congressional Democrats on a conference call she believed an agreement could be reached on Monday night, and Majority Leader Steny Hoyer said a vote was possible on the House of Representatives floor on Wednesday, according to a Democratic aide familiar with the call.

President Donald Trump told a White House news briefing he hoped congressional negotiators would reach a deal soon.

"A lot of progress has been made on that," he said.

A deal would end a stalemate over Trump's request to add to a small-business loan program. Congress set up the program last month as part of a $2.3 trillion coronavirus economic relief plan, but it has already run out of money.

McConnell complained that an agreement had not been reached because "our Democratic colleagues are still prolonging their discussions with the (Trump) administration."