But since Mr. Wheeler stepped in, he has raised concerns about the legality of the proposal as it is written, according to at least four people familiar with the matter. Privately, even some auto executives have also asked Mr. Trump to pull back from such an aggressive rollback, fearing that the lawsuits it will create could lead to years of regulatory uncertainty.
But Mr. Rosen, the deputy secretary of the Transportation Department, is confident that the proposal will stand up to legal challenge in part because of the changing makeup of the Supreme Court, according to a half-dozen people familiar with his thinking. With the retirement of the Supreme Court Justice Anthony M. Kennedy, who often served as a swing vote on the court, Mr. Trump has nominated a judge to succeed him, Brett Kavanaugh, who is considered more reliably conservative.
Mr. Rosen, a lawyer whose former clients have included General Motors and Hyundai, served as general counsel for the Transportation Department during the George W. Bush administration, where he was known as an opponent of efforts to combat climate change and regulate auto pollution. The plan would strip away regulations that he has fought for years.
“The thinking is, whatever they do to relax the standards, California will sue,” said Myron Ebell, who led the Trump administration’s E.P.A. transition team. “So why not go for the whole thing?”
Jody Freeman, a professor of environmental law at Harvard and a former adviser to President Barack Obama, noted that previous efforts to pre-empt such state-level authority have failed. “We’ve never seen a state-level waiver being revoked, and it’s not clear how that would work,” Ms. Freeman said.
Once the rule is made public, the E.P.A. and Transportation Department will take public comments before revising it and publishing a final rule this year. People who have spoken with Mr. Wheeler say they expect to see his more cautious approach reflected in a final rule that is less radical but more legally defensible.
And they note that even as on Thursday Mr. Wheeler walked back Mr. Pruitt’s move not to enforce pollution rules for “glider” trucks, he also wrote a memo saying that he intended to revisit the policy.
“He didn’t say, I’m abandoning this whole effort,” Professor Revesz said. “The last sentence of his memo is essentially saying, ‘We’ll still proceed full steam ahead.’ He’s just going to find a way to proceed more cautiously. His style is different, but ultimately he’s pursuing the same aim.”
