Attempts to remove Kepone-contaminated sediments from Virginia's James River could cost as much as $7.2 billion and "may not be technically feasible or financially possible," a U.S. study warned yesterday.

Two and one-half years after state health authorities closed a small plant that discharged massive amounts of the highly toxic pesticide into the river, Kepone continues to plague Hopewell, the small central Virginia city where it was made, according to the Environmental Protection Agency.

Kepone remains in the city's sewage system, on its soil, and, most persistently, on the bottom of the James River. There may be between 21,000 and 42,000 pounds of the pesticide in the river and removing it by dredging may be prohibitively expensive, the EPA said in a draft report.

"At the current rate it will take 50 to 100 years for the James River to cleanse itself," according to an accompanying scientific report also released yesterday. Until then, the report said fish taken from the river "will continue to carry Kepone concentrations" higher than recommended for human consumption.

The EPA report does not recom mend any specific course of action for either state or federal officials, but catalogues remedies to the widespread contamination and lists the costs of such actions. It will be up to EPA administrator Douglas M. Costle to recommend future steps to the governors of Maryland and Virginia and the federal government later this year after a final EPA report is issued.

Despite a finding that Kepone is likely to continue to contaminate fish in the James River for years, the EPA report says the pesticide "does not imminently threaten the Chesapeake Bay fisheries."

The bay is a much more economically important fishery than the James and there had been fears that Kepone would migrate down the James River, ultimately contaminating the bay. According to the EPA, that does not seem likely, but the report says continuous monitoring of the bay is needed to detect "any unsuspected movement" of Kepone.

Both the EPA report and an accompanying $800,000 research study released yesterday confirmed what scientists long have said about the persistence of Kepone in the environment. However, the report indicated that a surprising amount of Kepone has remained in Hopewell despite widely publicized efforts to clean the small converted service station where much of the powdery, white chemical was manufactured.

Relatively high amounts of the chemical remain in the earth around the plant and in the city's sewage lines, the reports say. The EPA draft urges consideration be given to removing earth from a park near the old Kepone plant site and other areas.

Kepone, washed from the clothes of plant workers and the plant itself has remained in the city's sewage lines, clinging to organic material in pipes throughout the town. The pesticide still enters the James River in levels higher than the EPA would have allowed, the report says. However, the reports say the amount now entering the river is insignificant compared to what is already there.