In all, a New York Times analysis, based on research from Harvard Law School, Columbia Law School and other sources, counts more than 60 environmental rules and regulations officially reversed, revoked or otherwise rolled back under Mr. Trump. An additional 34 rollbacks are still in progress.

With elections looming, the administration has sought to wrap up some of its biggest regulatory priorities quickly, said Hana V. Vizcarra, a staff attorney at Harvard Law School’s Environmental and Energy Law Program. Further delays could leave the new rules vulnerable to reversal under the Congressional Review Act if Democrats are able to retake Congress and the White House in November, she said.

The bulk of the rollbacks identified by the Times have been carried out by the Environmental Protection Agency, which repealed and replaced the Obama-era emissions rules for power plants and vehicles; weakened protections for more than half the nation's wetlands; and withdrew the legal justification for restricting mercury emissions from power plants.

At the same time, the Interior Department has worked to open up more land for oil and gas leasing by cutting back protected areas and limiting wildlife protections.

“Over the past three years, we have fulfilled President Trump’s promises to provide certainty for states, tribes, and local governments,” a spokeswoman for the E.P.A. said in a statement to The Times, adding that the agency was “delivering on President Trump’s commitment to return the agency to its core mission: Providing cleaner air, water and land to the American people.”

But environmental and legal groups said the rollbacks have not served that mission. Ms. Vizcarra, who has tracked environmental rollbacks for Harvard since 2018, said the agency under Mr. Trump has often limited its own power to regulate environmental harm, especially when it comes to climate change.

Many of the rollbacks have faced legal challenges by states, environmental groups and others, and some could remain mired in court beyond November, regardless of the outcome of the election.

Hillary Aidun, who tracks deregulation at Columbia University’s Sabin Center for Climate Change Law, said many of the rollbacks had not been adequately justified, leaving them vulnerable to legal challenge.

The New York Times analysis identified 10 rules that were initially reversed or suspended but later reinstated, often following lawsuits and other challenges. Other rollbacks were rebuffed by the courts but later revised by the administration and remain in effect.

All told, the Trump administration’s environmental rollbacks could significantly increase greenhouse gas emissions and lead to thousands of extra deaths from poor air quality each year, according to energy and legal analysts.

Below, we have summarized each rule that has been targeted for reversal over the past three years.