WASHINGTON — In the final hours of Scott Pruitt’s tenure as administrator, the Environmental Protection Agency moved on Friday to effectively grant a loophole that will allow a major increase in the manufacturing of a diesel freight truck that produces as much as 55 times the air pollution as trucks that have modern emissions controls.

The move by the E.P.A. came after intense lobbying by a small set of manufacturers that sell glider trucks, which use old engines built before new technologies significantly reduced emissions of particulates and nitrogen oxide that are blamed for asthma, lung cancer and other ailments.

It was just as strongly opposed by an unusual alliance of public health groups like the American Lung Association, environmental groups like the Environmental Defense Fund and major industry players like United Parcel Service, the largest truck fleet owner, and Volvo Group, one of the largest truck manufacturers.

The shift in agency policy came quietly late Friday, the last day of work for Mr. Pruitt, who resigned after several ethics scandals. But agency officials confirmed to The New York Times that, through the end of 2019, the E.P.A. will not enforce an annual cap of 300 gliders per manufacturer that had been imposed in January.