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 (EPA) on Monday reverse more lax standards passed under former president Donald Trump governing how far an automaker's cars must be able to travel on a gallon of gasoline, 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," 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 under 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."

US President Joe Biden, seen here driving an electric Jeep Wrangler Rubicon 4xe, has made fighting climate change a priority, and announced new standards that would raise average fuel efficiency for cars and trucks to cut emissions
US President Joe Biden, seen here driving an electric Jeep Wrangler Rubicon 4xe, has made fighting climate change a priority, and announced new standards that would raise average fuel efficiency for cars and trucks to cut emissions AFP / JIM WATSON

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.

The transportation sector is the biggest source of carbon emissions in the country, and the EPA said the new regulations would remove more than three billion tons of greenhouse gas 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 Detroit automakers have stepped up plans for electric vehicle production in recent months, and in a statement, Ford, which is investing billions in a bid to lead the shift to electric vehicles from fossil fuel-burning cars, hailed the White House's move.

"We applaud EPA's efforts to strengthen greenhouse gas emissions standards and create a consistent national plan that sets the United States on a path to a zero-emissions transportation future in alignment with the Paris Climate Agreement," the company said in a statement.

However, the Union of Concerned Scientists urged tougher action, with its president Johanna Chao Kreilick saying, "The new standards go a long way to undoing the damage done by the previous administration, but to stem climate catastrophe we must set our ambitions higher and demand more."

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.