Under President Biden, the Environmental Protection Agency has closed fewer civil cases against polluters than any administration in the last two decades and has overseen a drop in criminal investigations of environmental crimes.

David M. Uhlmann hopes to change that.

Mr. Uhlmann, 60, begins a new job this week as the agency’s top cop. An expert on environmental law, Mr. Uhlmann is leading the E.P.A. unit that holds companies and individuals accountable for fouling drinking water, dumping hazardous waste, failing to control toxic pollution and other violations.

A onetime federal prosecutor who spent seven years as chief of the environmental crimes section at the Department of Justice, Mr. Uhlmann was the lead attorney on the country’s first environmental justice criminal trial and later won the longest jail sentence in history for an environmental crime.

Mr. Uhlmann, whose confirmation as an assistant E.P.A. administrator was stalled in Congress for more than two years, enters the role at a consequential moment for the Biden administration.

The president has made bold promises to hold polluters accountable, particularly in low-income communities that have faced disproportionate levels of environmental contamination.

But a recent study found that the White House’s signature environmental justice program may not shrink racial disparities when it comes to exposure to pollution. And last month, the E.P.A. closed an investigation in into complaints from environmental groups that Louisiana had discriminated against Black communities in the way it issued permits for chemical plants in a majority-Black area known as Cancer Alley. In May, the state challenged the investigation in court, saying the E.P.A. had overstepped its authority. The following month, the E.P.A. closed the case.

In his first interview since his July 20 confirmation, Mr. Uhlmann said he was intent on increasing the number of administrative actions as well as the criminal and civil cases that the E.P.A. brings for violations of environmental law.

“The enforcement programs at E.P.A. are a force to be reckoned with, we are going to be present in every community across America where violations of the law are occurring,” said Mr. Uhlmann, who took a leave from teaching at the University of Michigan Law School to join the E.P.A. “We are going to hold polluters accountable when they break the law.”

On Thursday the E.P.A. intends to announce enforcement priorities, with a new emphasis on greenhouse gas emissions. The agency said it would focus on making sure that oil and gas wells, landfills and other facilities did not leak methane, a powerful greenhouse gas. It will also monitor the phase-down of another class of greenhouse gases, hydrofluorocarbons, or HFCs, which are used in air-conditioning and refrigeration. The United States and other countries have agreed to cut back production and use of HFCs by 85 percent over the next 13 years.

Other enforcement priorities include a focus on the toxic “forever chemicals,” perfluoroalkyl and polyfluoroalkyl compounds known as PFAS, as well as the disposal of coal ash, the toxic material left over from burning coal.

Mr. Uhlmann’s biggest challenge is “getting cases on the ground and filed,” said Richard Lazarus, a professor of environmental law at Harvard University. “He’s got a year and a half to realize the promise of these announcements. My guess is he’s impatient and ready to go.”

During the Trump administration, Mr. Uhlmann criticized the E.P.A.’s enforcement activity, which sank to record lows in terms of inspections and the volume of civil cases concluded as well as those referred for prosecution.

But that activity has not increased significantly since Mr. Biden took office.

While the E.P.A. has recently stepped up inspections, the number of civil cases resolved in fiscal year 2022 was the lowest in at least two decades, according to agency data. Most environmental violations are civil offenses, with enforcement action initiated by states or the E.P.A. They usually result in fines and other obligations to clean polluted areas and comply with the law.

The E.P.A. enforcement unit refers severe or deliberate violations to the Justice Department for criminal prosecution. Last year, the agency opened 117 criminal investigations, the second smallest number of inquiries in 22 years. (Only 115 investigations such were opened in 2017).

Mr. Uhlmann blamed the lingering effects of budget cuts and staff departures that occurred during the Trump administration.

The number of people working in E.P.A.’s civil enforcement program fell from 3,294 in 2012 to 2,253 in 2022, according to the Environmental Integrity Project, a watchdog group. The agency also has lost about 40 criminal enforcement agents since 2012 and seen a 30 percent budget cut over the last decade.

“If you experienced those kinds of cuts, it’s going to dramatically reduce how much you can do on behalf of communities across America to address harmful pollution, and the budget cuts did have that effect,” Mr. Uhlmann said.

The unit is rebuilding, he said, and the E.P.A. is hiring to try to fill more than 100 positions. Early 2023 data provided by the E.P.A. also showed more than 9,000 inspections have occurred, with more than half taking place in disadvantaged communities that the agency has pledged to prioritize.

Susan Bodine, who led E.P.A. enforcement in the Trump administration, said enforcement numbers were a lagging indicator of the work being done, and not entirely reflective of the significance of cases being brought. “Getting numbers up is easy, but it may not be meaningful,” Ms. Bodine said.

Eric Schaeffer, executive director of the Environmental Integrity Project, said there have been encouraging signs recently. In May, BP, the oil giant, agreed to pay a record $40 million penalty and spend about $200 million on environmental controls to settle civil claims brought by the E.P.A. and Justice Department that BP released excessive amounts of cancer-causing benzene in wastewater from its Indiana oil refinery.

But he also said Mr. Uhlmann needed to rebound far more aggressively.

“The laws don’t mean squat if they’re not enforced,” Mr. Schaeffer said. “You need a person in enforcement that wants to enforce and is not looking over their shoulder constantly that is looking at shadows and worrying what the politicians will say. I have a sense that David will do that.”

In his law school classes, Mr. Uhlmann often mined the cases he worked on during his 17 year career as a federal prosecutor.

In 1997 he brought what later would be called the first environmental justice criminal case, United States v. Jonnie James Williams. Mr. Williams, the owner of a Memphis company that refurbished metal drums, was sentenced to three years and four months for illegal storage and disposal of hazardous waste after neighbors complained of noxious fumes that wafted into their yards.

Mr. Uhlmann’s most notable case, in 2000, was against the owner of a fertilizer manufacturing company in Idaho who ordered his employees to clean out a storage tank containing cyanide without taking safety precautions. One worker was overcome by hydrogen cyanide gas while cleaning the tank and sustained permanent brain damage.

It resulted in a 17-year jail sentence, which at the time was the longest sentence ever imposed for an environmental crime.

George Breitsameter, a former U.S. attorney in Idaho who helped prosecute that case, said Mr. Uhlmann avoided ruffling feathers on a case that required coordination between state, local and federal authorities.

But when it came to the prosecution, Mr. Breitsameter said: “David is very aggressive. I would describe him as aggressive and fair.”

Mr. Uhlmann said that he hoped to breathe new life into the E.P.A.’s mission to uphold the nation’s environmental laws.

“Certainly my top priority is revitalizing the enforcement program at E.P.A. and doing everything I can, not just to bring it back, but to take it to new heights,” he said.