DETROIT — Four years ago, the American auto industry was so opposed to higher fuel economy standards that executives of Detroit camped out in Washington in an unsuccessful bid to undercut them.

On Friday, when President Obama announced even stricter standards — in fact, the largest increase in mileage requirements since the government began regulating consumption of gasoline by cars in the 1970s — the chief executives of Detroit’s Big Three were in Washington again.

But this time they were standing in solidarity with the president, who was also surrounded by some of Detroit’s highest-tech — and most fuel-efficient — new vehicles.

While the American carmakers, as well as their Asian rivals, once argued against even minimal increases in government fuel rules, they are acquiescing without protest to an increase to 54.5 miles per gallon by 2025, from the current 27 miles per gallon.