President Joe Biden is raising mileage standards for cars and trucks sold in the United States in a bid to limit emissions, as the spending bill he counted on to fund the fight against climate change appears to be on life support.

The new regulations announced by the Environmental Protection Agency on Monday reverse more lax fuel standards under Donald Trump, and show how Biden's White House is using regulatory power to curb emissions.

The announcement comes as the president's Build Back Better (BBB) social spending plan may have suffered a mortal blow after a crucial Democratic senator said he would not support the $1.75 trillion proposal.

"We followed the science, we listened to stakeholders and we are setting robust and rigorous standards that will aggressively reduce the pollution that is harming people and our planet -- and save families money at the same time," Environmental Protection Agency (EPA) Administrator Michael Regan said when announcing the standards.

Under the new EPA rules, the average fleetwide fuel consumption standards would be phased in over three years from 2023 and rise to 55 miles per gallon by 2026.

That is up from 43 miles per gallon under regulations enacted Trump last year, and the EPA estimates the new standards will save Americans between $210 and $420 billion on fuel costs by 2050.

US automakers have already announced major investments in electric vehicles and more fuel-efficient cars, but industry group the Alliance for Automotive Innovation warned the new standards will be hard to meet without help from the government.

The "EPA's final rule for greenhouse gas emissions is even more aggressive than originally proposed, requiring a substantial increase in electric vehicle sales, well above the four percent of all light-duty sales today," its president John Bozzella said.

"Achieving the goals of this final rule will undoubtedly require enactment of supportive governmental policies -– including consumer incentives, substantial infrastructure growth, fleet requirements and support for US manufacturing and supply chain development."

Shifting standards

In contrast with Trump, Biden has made fighting climate change a priority for his administration, and was counting on BBB's passage to pay for expansive programs aimed at doing that.

But Democratic Senator Joe Manchin announced Sunday he would not vote for the bill, imperiling its passage in a Senate where Biden needs the vote of every Democrat to get legislation past Republican objections.

Emissions standards are one of Washington's most direct ways to act against pollution, and the EPA said the new regulations would remove more than three billion tons of greenhouse gas emissions by 2050.

The EPA also predicted that compared to cost increases to meet the standard, consumers will save about $1,000 through lower fuel prices over the lifetime of the average 2026 year vehicle.

The new rule sets targets similar to regulations promulgated under former president Barack Obama, but the Trump administration reversed those, arguing they would drive up car prices and encourage people to drive older vehicles for longer.

That sparked a fight with most populous US state California, where its Democratic leadership tried to implement its own, stricter standards on car emissions.