President Joe Biden made an impassioned plea in his birthplace of Scranton on Wednesday for massive spending on US infrastructure and social safety nets, as his Democratic party continued to feud over the price tag.

"America is still the largest economy … but we risk losing our edge as a nation," Biden said, describing the gap between US modernization of its infrastructure compared to competitors. "We haven't passed an infrastructure bill for decades."

The two bills under debate -- one for repairing infrastructure and another to fund childcare and other social spending -- will "breathe new life into the economy," Biden said in his speech at a museum for trolley trains in the blue collar Pennsylvania town where he spent part of his childhood.

The bills remain stuck in Congress, where Democrats control both houses with razor-thin majorities but are divided between themselves on the cost and scope of Biden's proposals.

There were positive signals on Wednesday, but no solid deal, with two key senators still holding back.

Biden showed his frustration, almost shouting in mid-speech: "This is the United States of America, damn it. What are we doing?"

But in an address filled with emotional references to his family's humble roots and connections to the working class, he predicted a happy ending for the two bills.

"This has been declared dead on arrival from the moment I introduced it, but I think we're going to surprise them," he said.

Still working on it

At stake are a $1.2 trillion bill for improving creaking US bridges, roads and railways and an even bigger splurge on childcare and other areas that Biden says will provide historic help to struggling ordinary Americans.

The main bone of contention is the size of the second package, with an initial figure endorsed by Biden of $3.5 trillion clearly dead.

The White House is now indicating it would settle for something between $1.9 and $2.2 trillion, while a leading moderate Democrat, Senator Joe Manchin, wants as little as $1.5 trillion. The ultimate top line may fall somewhere between.

That means making significant cuts to Biden's priorities in areas like expanding free education and clean energy.

Senator Chuck Schumer, who heads the Democrats' tiny majority in the Senate, fueled expectations that a deal may be imminent.

"We are getting closer to an agreement. We want to finalize a deal by the end of this week," he said Wednesday.

"Everyone is going to have to compromise if we are to find that legislative sweet spot that we can all get behind," Schumer said.

But with Manchin and another reluctant Democratic senator, Kyrsten Sinema, still not on board, the White House remained cautious.

"We've made a lot of progress but we still have work to do," Biden's senior adviser Cedric Richmond told CNN.

Biden's Scranton speech was meant to remind his party that he beat Donald Trump last year in part by wooing blue collar workers.

"Both these bills were all that I talked about. But guess what? Eighty one million people voted for me. More people voted than any time in American history and their voices deserve to be heard," he said.

Midterm legislative elections in just over a year could see the Democrats lose their majorities in one or both chambers to the Republicans, meaning Biden's spending plans are unlikely to get a second chance.