The Environmental Protection Agency's pursuit of criminal cases against polluters has dropped off sharply during the Bush administration, with the number of prosecutions, new investigations and total convictions all down by more than a third, according to Justice Department and EPA data.

The number of civil lawsuits filed against defendants who refuse to settle environmental cases was down nearly 70 percent between fiscal years 2002 and 2006, compared with a four-year period in the late 1990s, according to those same statistics.

Critics of the agency say its flagging efforts have emboldened polluters to flout U.S. environmental laws, threatening progress in cleaning the air, protecting wildlife, eliminating hazardous materials, and countless other endeavors overseen by the EPA.

"You don't get cleanup, and you don't get deterrence," said Eric Schaeffer, who resigned as director of the EPA's Office of Civil Enforcement in 2002 to protest the administration's approach to enforcement and now heads the Environmental Integrity Project, a watchdog group. "I don't think this is a problem with agents in the field. They're capable of doing the work. They lack the political support they used to be able to count on, especially in the White House."

The slower pace of enforcement mirrors a decline in resources for pursuing environmental wrongdoing. The EPA now employs 172 investigators in its Criminal Investigation Division, below the minimum of 200 agents required by the 1990 Pollution Prosecution Act, signed by President George H.W. Bush.

The actual number of investigators available at any time is even smaller, agents said, because they sometimes are diverted to other duties, such as service on EPA Administrator Stephen L. Johnson's eight-person security detail.

Johnson, President Bush's chief environmental regulator, foreshadowed a less confrontational approach toward enforcement when he served as the EPA's top deputy in late 2004. "The days of the guns and badges are over," Johnson told a group of farm producers in Georgia the day before Bush won reelection, according to a news account of the speech.

Administration officials said they are not ignoring the environment but are focusing on major cases that secure more convictions against bigger players.

"We have been on an unprecedented run of success in the enforcement arena," said Granta Y. Nakayama, EPA assistant administrator for enforcement and compliance assurance. "These are major cases we are pursuing."

Nakayama said that, in the past three fiscal years, the EPA has cut between 890 million and 1.1 billion pounds of air pollution through enforcement, making them "three of the four highest years in the agency's history. . . . You're seeing, I think, a historic period in terms of getting pollution out of the air."

He added that he hopes to boost the number of criminal investigators and said that, over the past five years, the agency has won convictions against 95 percent of the people indicted for environmental crimes.

Administration officials acknowledge taking a new approach to environmental enforcement by seeking more settlements and plea bargains that require pollution reductions through new equipment purchases or participation in EPA compliance programs.