Farmers, real estate developers and golf course owners protested vociferously in 2015 when the Obama administration put forth its clean-water regulation, which took an existing federal prohibition on pollution in major public waters, like the Chesapeake Bay and Puget Sound, and expanded that protection to include the streams, tributaries and wetlands that flow into those waters.

A regulation protecting large public water bodies is legally required under the Clean Water Act. But there have been decades of legal battles over how expansive such a regulation should be. The Obama administration’s regulation took a wide view of how far the federal government could go in its effort to protect waters; Mr. Trump directed Mr. Pruitt to take a far narrower view of the law.

In his 2017 executive order directing Mr. Pruitt to rework the clean water regulation, Mr. Trump told Mr. Pruitt to be guided by the views of Antonin Scalia, the conservative Supreme Court justice who died in 2016. In a 2006 opinion in the case Rapanos v. United States, Justice Scalia argued for an extremely narrow interpretation of the Clean Water Act, one that protected only major water bodies and the water that flowed into them from continuously running tributaries.

It is widely believed that Justice Scalia’s opinion has shaped Mr. Pruitt’s forthcoming proposal, according to people familiar with the plan. It would regulate pollution only in large, public bodies of water, and in permanent streams and tributaries that drain into them. Exempt from regulation would be seasonal streams, water bodies that flow in some portions of the year but not others.

Environmental groups say Mr. Pruitt’s expected proposal will mean dirtier water. “Roughly 60 percent of the stream miles in the U.S. are intermittent, so if that’s what the proposal cuts out, it will make it easier for polluters to dump in them,” said Jonathan Devine, an expert in clean water law at the Natural Resources Defense Council, an advocacy group.

The Obama rule, if implemented, could have prevented farmers and developers — particularly of water-rich properties like golf courses — from using chemical fertilizers and pesticides that might have drained into streams and wetlands. In particular, opponents complained, the rule could have required farmers and other property owners to register for E.P.A. permits to use such chemicals on their land even if the land did not directly abut a major water body.

The anger among farmers fed directly into the populism that helped drive Mr. Trump into office, and he has seized upon it as a rallying cry.

“Really, they were trying to regulate land use,” said Donald Parrish, director of regulatory relations with the American Farm Bureau Federation. “It would have called into question where and how farmers could use things like manure spreaders and pesticide sprayers. Or how deeply they could plow. Or even what kinds of crops could be grown where.”