– One of the main advancements of the past half-century at coal-burning power plants has been the “scrubber,” a clean-air device that played a major role in ending the acid-rain crisis of the 1970s and that removes millions of tons a year of a pollutant blamed for respiratory disease.

However, the Trump administration’s proposed rewrite of climate-change regulations could enable some of the United States’ dirtiest remaining coal plants to be refurbished and keep running for years without adding scrubbers or other modern pollution controls.

Industry lawyers and former federal officials say the policy shift is one of the most consequential pieces of the Environmental Protection Agency’s proposal, made public this week, to replace the Obama-era Clean Power Plan, which was designed to slow the pace of climate change in part by encouraging the retirement of older coal plants and a shift toward greener energy sources.

“This is a power plant life-extension rule masquerading as a climate rule,” said Kate Konschnik, a Bush-era Department of Justice lawyer who handled lawsuits against coal-burning power plants, which she said would now become much harder to file.

An EPA spokesman, Michael Abboud, defended the policy change, saying in a statement it was designed to benefit the environment and intended “to further encourage efficiency improvements at existing power plants.”

About 30 percent of the nation’s coal-burning power plant units now do not have scrubbers, devices that use a cloud of fine water droplets, along with crushed limestone, to pull sulfur out of the plant’s exhaust before it reaches the atmosphere. Another 22 percent of plants do not have advanced nitrogen oxide controls that limit smog.

Many of these older plants benefited from a grandfathering provision in federal law that didn’t require them to add advanced pollution controls unless they underwent major renovations.

Under today’s rules, such major retrofits of old plants often come with a big demand: The owners must also spend hundreds of millions of dollars to upgrade the air-pollution equipment to the best available technology, including scrubbers.

The proposed rule change would let older plants be updated with newer and more efficient working components like boiler feed pumps and steam turbine upgrades, potentially extending their operating lives for years, while allowing them to avoid the requirement for the updated pollution controls.

The rules could benefit plants like the Gerald Gentleman Station in Sutherland, Neb., the state’s largest power generating plant, which started operating in 1979. The plant lacks both scrubbers for sulfur oxides and what is known as selective catalytic reduction for nitrogen oxides. As of 2017, its two power units were emitting more than 21,000 tons of sulfur dioxide per year, according to EPA data.

The company intends to keep the plant operating by upgrading various critical pieces of its electricity generation equipment, but has estimated that installing the most modern pollution control devices would cost an estimated $1.5 billion. The new rule could create a clear path for the plant to upgrade without facing a giant air-pollution cleanup order.

“This really should help clear up some of that uncertainty on the ability to do efficiency projects,” said Joe Citta, environmental manager at Nebraska Public Power District, which runs the plant. “That should be helpful.”

Sulfur oxides are harmful to the human respiratory system. They can also react with other contaminants to create so-called particulate matter, which can penetrate deeply into the lungs and cause additional health problems.

The new policy will almost certainly be challenged by environmental groups in court. They, along with some state-government officials, call the change a step backward for the Clean Air Act.

“This is going to mean dirtier air and hurt Americans through a loophole built on a lie that pollution from these plants will not get worse,” said John Walke, clean air director at the Natural Resources Defense Council.