A federal study of workers at the Savannah River nuclear plant found twice the usual rate of deaths from leukemia. The finding by the Oak Ridge Associated Universities Center for Epidemiologic Research is consistent with the results of astudy by the Du Pont Co. released in 1976, plant officials said in a statement Wednesday. Du Pont runs the federal plant under contract. The Oak Ridge S.C., study included 1,274 male hourly workers who were hired before 1955 and worked fiveto 15 years. Overall, they had fewer than expected deaths from all causes, but six leukemia deaths, a greater number than would be expected.