WASHINGTON — The Obama administration will seek tougher fuel-economy standards for the nation’s heavy trucks and buses as part of its expanded effort to cut down on pollutants blamed for the warming of the planet, officials said Friday.

A proposed regulation would phase in higher efficiency requirements for heavy-duty engines beginning in the model year 2021, eventually leading to a 24-percent improvement in mileage compared to similar vehicles built to meet today’s standards, the officials said.

The proposal is the latest in a series of moves intended to slash emissions of greenhouse gases, coming on the heels of previously announced efforts to curb pollution from cars and light trucks, aircraft and power plants. The White House has pledged to reduce overall emissions in the United States by at least 26 percent by the year 2030, compared to 2005 levels.

Unlike some of the earlier steps, the proposed rules are backed by many in the trucking industry as a way to lower fuel costs borne by drivers and, ultimately, by consumers. Administration officials said the measures, if finalized, could reduce spending on gasoline and diesel by an estimated $170 billion.

“Once upon a time, to be pro-environment, you had to be anti-big-vehicles. This rule will change that,” said Transportation Secretary Anthony Foxx, who announced the proposal jointly with officials of the Environmental Protection Agency. “In fact, these efficiency standards are good for the environment, and the economy.”

The proposed regulation affects a class of vehicles that includes the largest tractor-trailers as well as buses, large pick-up trucks and vans. These heavy- and medium-duty vehicles represent only about 5 percent of total highway traffic but account for 20 percent of fuel consumption and carbon emissions.

The EPA said the proposals, if finalized, would reduce oil consumption by nearly 2 billion barrels and lower carbon emissions by 1 billion metric tons. The new standards would raise vehicle prices by as much $14,000 for a large truck, according to agency projections, but the higher sticker price would be offset by fuel savings in about two years, EPA officials said.

The measures also include tougher standards for trailers, to improve fuel economy.

The proposals overall will “save consumers, businesses and truck owners money,” EPA Administrator Gina McCarthy said, “and at the same time spur technology innovation and job-growth, while protecting Americans’ health and our environment over the long haul.”

The reaction among truckers’ groups was mostly positive, though some expressed concerns about whether the technology needed for improved fuel economy was fully in place.