WASHINGTON — Mitt Romney, true to his roots as the son of an auto executive, was talking about cars.

It was May 2006. Mr. Romney, the Massachusetts governor, was chatting up his Montana counterpart about his vision for an energy-efficient car of the future — lightweight and narrow, with tandem-style seating, so that two vehicles could drive side by side in one highway lane.

“He was getting animated about all these little cars that would be driving around in these lanes,” Brian Schweitzer, the Montana governor, recalled in an interview. Mr. Schweitzer, a Democrat, laughed, thinking about how Republicans might react. “I said, ‘Mitt, if you ever run for president, don’t ever talk about that again.’ ”

Today, as the Republican nominee for president, Mr. Romney is far more apt to talk about oil drilling than energy-efficient cars. He has presented a plan to open up more land and coastline to oil and gas drilling, grant speedy approval to the Keystone pipeline to transport crude oil from Canada to the United States, end wind and solar power subsidies and curb regulations that discourage burning coal for electricity. It is an agenda far different from the one he outlined in his early days as governor.