"A lot goes on when you are campaigning," Wagoner said last week at a Washington breakfast. "I'm not resigned" to states getting to impose their own rules, he said.
Republican John McCain and Democrats Hillary Clinton and Barack Obama say they favor state rules.
Reaction to Wagoner's remarks was not available from the candidates. But environmental activist Frank O'Donnell said he expects the next president to reverse the Bush administration's decision to block state rules.
States' rights on climate issues has become a "sacred cow," especially for House Speaker Nancy Pelosi, D-Calif., said O'Donnell, president of Clean Air Watch.
Wagoner said a top priority of the next president will be economic growth, and leaders realize the auto industry is an important driver of economic activity.
Automakers and allies say state rules would create market chaos. California regulators have calculated that their rules would require vehicles to average about 40 mpg by 2020.
Wagoner said the industry already is challenged to meet a new federal fuel economy standard: 35 mpg by the 2020 model year.
But Wagoner also appeared to distance himself from the assertion that the industry favored that tougher national standard. He started to say, "We signed up" for higher fuel economy standards. Then he corrected himself to say, "We were signed up for a very aggressive" new national standard.
At another point, Wagoner noted automakers backed the bill enacted last December. He referred to the Alliance of Automobile Manufacturers, which represents GM, Toyota, Ford, Chrysler and six other automakers.
Wagoner also disavowed a remark by GM Vice Chairman Bob Lutz that global warming is a "crock."
Wagoner said the remark does not represent GM's position. But he stopped short of saying motor vehicles contribute to climate change.