Kepone pollution in the James River is so severe and the costs of a cleanup so "enormous" that no full-scale effort should be attempted to rid Virginia's major river of the toxic pesticide, the Environmental Protection Agency has concluded.

The report released yesterday also affirmed previous statements that it would be "decades" - perhaps 50 to 100 years - before the river cleans itself sufficiently to allow safe consumption of its fish and shellfish.

While the EPA conclusions were gloomy for Virginia, Maryland officials could only be pleased with a clean bill of health the study gave the Chesapeake Bay.

The study, forwarded to Acting Gov. Blair Lee III of Maryland and Gov. John N. Dalton of Virginia on Thursday, found that "the data indicate no imminent danger of Kepone contamination to the Chesapeake Bay at this time."

"Kepone sediment contamination of Chesapeake Bay is not evident" and Kepone contamination toward the bay."

EPA Acting Administrator Barbara Blum also asked for creation of a state-federal advisory task force to continue surveillance of the chlorinated hydrocarbon pesticide, which was discharged into the river from manufacturing operations in Hope-well, Va., from 1966 to 1975. EPA concluded that there are 20,000 to 38,000 pounds of Kepone in the top foot of James River sediment.

Cleaning the river bottom would require removal of sediment from 200 square miles of river bottom at a cost of billions of dollars, the study said. And the study said, the dredging's impact on the river is unknown.

EPA said that future Army Corps of Engineers dredging to keep the river navigable should be done with a special Japanese dredge called an oozer dredge. But one ERA official said that there was no such dredge now working in the United States.

The oozer dredge picks up sediment without stirring up the bottom and spreading pollution, the official said. The EPA study said that along with using the special dredge, the present policy of dumping the river spoil back into other parts of the river should be abandoned.

Kepone-contaiminated spoils should be placed in protected spoil sites developed along the river, according to the study. To protect the bay, a longterm emergency strategy to prevent Kepone movement from storms or other natural disasters should be developed and study should be given to possible use of submerged silt dams in the lower James, the EPA concluded.

The EPA also found considerable residual Kepon in the soil around Hopewell but said that the human health effects from the residues have not been determined. It said this question should be investigated further and that elimination of Kepone-contaminated sludge and soil through incineration or other means should be expedited.

Allied Chemical Corp., which began manufacture of Kepone in Hopewell, has been seeking governmental clearance to burn Kepon wastes at a faciality in Great Britain.

Blum warned that the study "does not provide recommendations that, if implemented, would bring an end to concern about the Kepone contamination problem in the James River." But she called the results "very beneficial in charting the direction for future surveillance and mitigation actions."

"It is evident that the problem bears continuing surveillance because the environemntal consequences of Kepone contamination...have the potential for impacting areasthat now are virtually uncontaminated," Blum said.