THE BURNED OVER DISTRICT

Not any puffed up pickups, but the real ones that haul goods all around this country. Having worked with industry to make new diesels cleaner than gasoline engines, the EPA wants to increase the mileage from a current average of 5/6 mpg to around 9 mpg, a huge jump for trucks.

This week, the E.P.A. is expected to propose regulations to cut greenhouse gas emissions from heavy-duty trucks, requiring that their fuel economy increase up to 40 percent by 2027, compared with levels in 2010, according to people briefed on the proposal. A tractor-trailer now averages five to six miles a gallon of diesel. The new regulations would seek to raise that average to as much as nine miles a gallon. A truck’s emissions can vary greatly, depending on how much it is carrying.

The hotly debated rules, which cover almost any truck larger than a standard pickup, are the latest in a stack of sweeping climate change policy measures on which President Obama hopes to build his environmental legacy. Already, his administration has proposed rules to cut emissions from power plants and has imposed significantly higher fuel efficiency standards on passenger vehicles.

The truck proposals could cut millions of tons of carbon dioxide pollution while saving millions of barrels of oil. Trucks now account for a quarter of all greenhouse gas emissions from vehicles in the United States, even though they make up only 4 percent of traffic, the E.P.A. says.

But the rules will also impose significant burdens on America’s trucking industry — the beating heart of the nation’s economy, hauling food, raw goods and other freight across the country.

It is expected that the new rules will add $12,000 to $14,000 to the manufacturing cost of a new tractor-trailer, although E.P.A. studies estimate that cost will be recouped after 18 months by fuel savings.

Environmental advocates say that without regulation, the contribution of American trucks to global warming will soar.

“Trucking is set to be a bad actor if we don’t do something now,” Jason Mathers, head of the Green Freight program at the Environmental Defense Fund.

But some in the trucking industry are wary.

“I’ll put it this way: We told them what we can do, but they haven’t told us what they plan to do,” said Tony Greszler, vice president for government relations for Volvo Group North America, one of the largest manufacturers of big trucks. “We have concerns with how this will play out.”

All concerned have a long haul ahead of them.