More: 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,"

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.

"Environmental crimes are simply not in the U.S. attorney top 10 priorities," said one senior EPA official, who spoke on the condition of anonymity because he is not authorized to talk to the news media.