By Coral Davenport

April 20, 2019 - A federal judge late Friday delivered a significant setback to the Trump administration’s policy of promoting coal, ruling that the Interior Department acted illegally when it sought to lift an Obama-era moratorium on coal mining on public lands.

The decision, by Judge Brian Morris of the United States District Court of the District of Montana, does not reinstate President Barack Obama’s 2016 freeze on new coal mining leases on public lands. That policy was part of an effort by the Obama administration to curtail the burning of coal, a major producer of greenhouse gases contributing to climate change.

But the court ruling does say that the 2017 Trump administration policy, enacted by former Interior Secretary Ryan Zinke, to overturn Mr. Obama’s coal mining ban did not include adequate studies of the environmental effects of the mining, as required by the National Environmental Policy Act of 1970, or NEPA, one of the nation’s bedrock environmental laws.

“Federal Defendants’ decision not to initiate the NEPA process proves arbitrary and capricious,” Judge Morris wrote.

The decision means that “the Interior Department has to go back to the drawing board if they want to continue to sell coal mining leases on public lands — they have to do a better job of legally and scientifically justifying this,” said Jenny Harbine, an attorney for Earthjustice, who took part in the oral arguments against the Trump administration.

The judge also told the plaintiffs and defendants that in the coming months he will put forth a second legal decision on whether the Obama-era mining ban should be reinstated.

A spokeswoman for the Interior Department, Faith Vander Voort, and Conor Bernstein, a spokesman for the National Mining Association, which joined with the Trump administration on the case, said they are reviewing the decision.

Mr. Trump, who campaigned on rolling back Mr. Obama’s environmental legacy, had in particular hoped to end his predecessor’s freeze on mining for coal on public land. More than 40 percent of the coal produced in the United States comes from federal land, and most of the planet-warming fossil fuel pollution comes from burning coal. Mr. Obama saw the effort to block coal mining on public land as a key step in tackling climate change, while Mr. Trump saw the lifting of that ban as a crucial step to help coal miners.

Efforts by Mr. Trump to deliver on his campaign promise to help the coal industry and roll back his predecessor’s signature environmental policies — particularly rules to curb oil and coal pollution, the chief causes of global warming — have repeatedly been blocked by the courts. Many have been denied for reasons similar to those given by Judge Morris in Friday’s decision: The administration did not follow correct legal protocol in justifying its actions.

This setback is the latest in what environmental law observers estimate is a string of about 40 such courtroom losses for efforts by Mr. Trump to undo Mr. Obama’s environmental rules.

On Friday, the United States Court of Appeals for the Ninth Circuit gave the Environmental Protection Agency 90 days to decide whether it will ban chlorpyrifos, a pesticide linked to brain damage. While the Obama administration had recommended banning the chemical, based on the recommendations of E.P.A. scientists, the Trump administration has sought to allow the agriculture industry to continue to use the chemical.

And last month a federal judge in Alaska ruled unlawful an executive order by Mr. Trump that lifted an Obama-era ban on oil and gas drilling in the Arctic Ocean and parts of the North Atlantic coast.

Fossil fuel advocates, however, have taken heart in the recent confirmation of Secretary of Interior David Bernhardt, an expert in natural resources law who previously worked as an oil lobbyist.

Mr. Bernhardt’s predecessor, Mr. Zinke, a former congressman and member of the Navy SEALs, was viewed as inexperienced with policy and legal matters. Mr. Bernhardt is known as a deeply experienced legal and policy expert, who as a lawyer argued major environmental and energy cases before federal courts.

“Bernhardt is a whole different thing,” said Patrick Parenteau, a professor of environmental law at Vermont Law School. “They’ve been in such a hurry to carry out orders and they’ve been cutting corners — they’ll probably clean that up.”