The final version of the standards is weaker than an initial proposal by the agency that automakers argued would be all but impossible to meet.

The fuel economy standards published Friday are designed to complement emissions rules set by the Environmental Protection Agency in March, and take into account efforts led by state regulators in California to spur the adoption of electric vehicles. Private cars and trucks are a major source of carbon emissions, and a key part of the Biden administration’s environmental agenda involves pushing for a dramatic increase in the number of battery-powered vehicles on roads.