WASHINGTON — Future semitrailers, school buses, delivery vans, garbage trucks and heavy-duty pickups must do better at the pump under first-ever fuel-efficiency rules coming from the Obama administration.

WASHINGTON — Future semitrailers, school buses, delivery vans, garbage trucks and heavy-duty pickups must do better at the pump under first-ever fuel-efficiency rules coming from the Obama administration.

The Environmental Protection Agency and the Transportation Department are moving ahead with a proposal for medium- and heavy-duty trucks, beginning with those sold in the 2014 model year and into the 2018 model year.

The plan is expected to seek about a 20 percent reduction in greenhouse-gas emissions and fuel consumption from longhaul trucks, according to people familiar with the plan. They spoke on condition of anonymity because they did not want to speak publicly before the official announcement, expected today.

Overall, the proposal is expected to seek reductions of 10 percent to 20 percent in fuel consumption and emissions based on the vehicle's size. Large semitrailers tend to be driven up to 150,000 miles a year, making them ripe for improved miles per gallon.

The rules will cover big rig semitrailers, "vocational trucks" such as garbage trucks and transit and school buses, and work trucks such as heavy-duty versions of the Ford F-Series, Dodge Ram and Chevrolet Silverado.

The White House has pushed for tougher fuel-economy standards across the nation's fleet as a way to reduce dependence on oil and cut greenhouse-gas emissions tied to global warming.

The fleet of new cars, pickups and SUVs will need to reach 35.5 mpg by 2016, and the government is developing plans for future vehicle models that could push the standards to 47 mpg to 62 mpg by 2025.