US senators on Sunday finalized a historic, trillion-dollar infrastructure proposal that is expected to be approved within days, Democratic Senate leader Chuck Schumer said.

If passed by Congress and signed into law, the bill would pump historic levels of federal funding into fixing US roads, bridges and waterways, ensuring broadband internet for all Americans and expanding clean energy programs.

A bipartisan group "finished writing the text of the infrastructure bill," Schumer told the Senate, which met for an extended weekend session in Washington.

"I believe the Senate can process relevant amendments and pass this bill in a matter of days."

The bill, a cornerstone of President Joe Biden's sweeping domestic agenda, is about 2,700 pages long and provides for $1 trillion in funding.

The Democratic leader succeeded in rallying a few elected officials from the opposite camp to work on the proposal.

The group released a joint statement saying the goal of the bill was to invest in infrastructure and create jobs without raising taxes.

"This bipartisan bill and our shared commitment to see it across the finish line is further proof that the Senate can work," the statement said.

The group consisted of Republicans Rob Portman, Susan Collins, Mitt Romney, Lisa Murkowski and Bill Cassidy, and Democrats Kyrsten Sinema, Joe Manchin, Mark Warner, Jeanne Shaheen and Jon Tester.

The bill would allow the largest-ever federal investments in public transit, as well as drinking and waste water infrastructure; the largest funding of passenger rail since the creation of Amtrak; and the largest investment in bridges since the nation's highway system was developed.

It would also help tackle the climate crisis by investing in energy projects, such as electric buses and a cleaner electricity grid.

Biden's other major economic and social challenge is to pass an ambitious $3.5-trillion budget package that includes once-in-a-generation spending on health care, education, social welfare and climate action.

But Democrats are not counting on any Republican support for that project.

Biden's big political project is for the United States to offer an alternative to the Chinese authoritarian model. This requires being at the forefront of innovation while also guaranteeing jobs and economic stability for the American middle class.