The Environmental Protection Agency has begun an investigation into whether it should bring pollution charges against a Virginia sewage treatment plant that was praised last month by Gov. John N. Dalton as an outstanding example of regional planning.

An EPA spokesman said yesterday that a special team from the agency's National Enforcement Investigating Center in Denver will begin an on-the-scene investigation today at a new Hopewell, Va., sewage plant.

The plant, dedicated last month by Dalton and other state officials, replaces a smaller plant that was knocked out of commission in 1975 when the highly toxic pesticide Kepone was discharged into the city's sewage system.

Built at a cost of $48 million, the new plant is designed to handle a heavy flow of industrial wastes from chemical pulp and other industries in the Hopewell area southeast of Richmond. State records indicate that the plant was been dumping excessive pollutants into the James River since it began operating in August 1977.

"They're (the investigative team, going in because of our concern that there may be violations of law," said EPA attorney Jed Callen. "There are already technical violations."

Although the staff of the State Water Control Board recommended legal action against Hopewell last winter, the five-member state board has given the city several extensions to permit it to bring the plant into compliance.

Norman M. Cole Jr. of Fairfax County, a former chairman of the water board and an adviser to Dalton in his race for governor last year, has cited the Hopewell pollution as an example of how lenient the state has become toward pollution from municipalities. Board officials have denied they are relaxing their standards because of pressure from local governments.

Callen said the EPA investigation was prompted by "the potential importance of the plant. We remember Kepone. It is a sensitive issue."