US President Joe Biden takes off his protective facemask as he arrives to speak at the 76th Session of the UN General Assembly on Tuesday in New York. This is the first speech to the world body by Biden. Photo: AFP

Joe Biden faces the most important test of his presidency this week as Democrats in the US Congress launch a highwire bid to implement his sweeping economic agenda while keeping the government's lights on.

The House and Senate are moving toward votes on legislation dealing with infrastructure and social programs worth almost $5 trillion while also averting a government shutdown on Friday and a looming debt default.

Failure on any front would be catastrophic for a president looking to cement his legacy, while Democrats would see their chances diminished for hanging onto the House of Representatives and Senate in next year's midterm elections.

"You know me: I'm born optimistic. I think things are going to go well. I think we're going to get it done," Biden told reporters at the White House.

At stake is the fate of Biden's $3.5 trillion Build Back Better social welfare package that only Democrats support, and a $1.2 trillion infrastructure bill to improve transport networks and broadband coverage.

Democratic House Speaker Nancy Pelosi told colleagues that there would be a vote on infrastructure on Thursday, the same day Congress needs to strike a funding deal to avoid a government shutdown.

Progressive Democrats have repeatedly threatened to tank infrastructure without a significant commitment from their moderate colleagues on Build Back Better.

Moderates nervous about freewheeling spending have said they may not vote for the bigger bill without infrastructure crossing the line first. 

"The next few days will be a time of intensity," Pelosi wrote to House Democrats, who have a three-vote margin in the House, plus the anticipated support of at least 10 Republicans for infrastructure.

Biden says the two bills would save the average family $15,000 a year through expanded care and education programs and reduced drug pricing, while transforming public transport, highways, bridges and broadband internet access would make life easier and greener. 

The president told reporters Monday that agreement on Build Back Better may not be completed before the infrastructure vote and shutdown deadline, as he added: "I hope it's by the end of the week."

Adding to the drama, lawmakers have until midnight going into Friday to green-light a package to fund the government ahead of federal agencies running out of money.

Biden, who discussed the bills via phone earlier Monday with Pelosi and Senate majority leader Chuck Schumer, slammed what he called Republican "actions that show a lack of concern about our economic recovery," according to a White House statement.

AFP