The Environmental Protection Agency, now regarded suspiciously by friends of various earths, has been moving to create a professional criminal enforcement staff to deal harshly with polluters, particularly the "midnight dumpers" of hazardous or toxic wastes.

The first investigator hired for the staff developed the case that resulted last week in a $2,500 fine and 90-day jail sentence for William Bushey, half-owner and vice president of the Corning Fibers Inc. paper company in Wells River, Vt. He pleaded guilty to conspiracy, willful contempt of court and violation of the Clean Water Act.

The story began in 1977 when EPA used its time-honored tactic of entering into a civil consent agreement with Corning Fibers under which the firm promised it would install certain pollution-control devices. In February, according to Peter Beeson, director of the new EPA Office of Criminal Enforcement, company employes told EPA's regional office in Boston that the company was discharging untreated pollutants directly into a nearby river. Once the investigator arrived, he also found that some equipment the company had promised in the consent decree to install had never been hooked up.

This is not the first time someone has gone to jail for an environmental violation, but it is rare, Beeson said. The Reagan administration job freeze slowed his efforts to hire investigators for the regional offices, he said, but that is now being accomplished. There will be 20 professional investigators nationwide.

William Sullivan, director of enforcement for EPA, said, "The only way we can get close to enforcing environmental laws is if people filing those reports look at them in the same way that they do their income tax." He said investigators will concentrate on false reporting in the clear hope that publicity will encourage other potential violators to abide by their consent decrees.