WASHINGTON — The Trump administration is expected on Tuesday to announce its final rule to rollback Obama-era automobile fuel efficiency standards, relaxing efforts to limit climate-warming tailpipe pollution and virtually undoing the government’s biggest effort to combat climate change.

The new rule, written by the Environmental Protection Agency and the Department of Transportation, would allow cars on American roads to emit nearly a billion tons more carbon dioxide over the lifetime of the vehicles than they would have under the Obama standards and hundreds of millions of tons more than will be emitted under standards being implemented in Europe and Asia.

Trump administration officials raced to complete the auto rule by this spring, even as the White House was consumed with responding to the coronavirus crisis. President Trump is expected to extol the rule, which will stand as one of the most consequential regulatory rollbacks of his administration, as a needed salve for an economy crippled by the pandemic.

The lower fuel-efficiency standard “is the single most important thing that the administration can do to fulfill President Trump’s campaign promise of reforming the regulatory state, and to undo the impact that the previous administration has had on the economy,” said Thomas J. Pyle, the president of the Institute for Energy Research, an organization that supports the use of fossil fuels.