Though billions of dollars have been spent on the cleanup of U.S. nuclear weapons sites, the Department of Energy is coming up short in the task because its bureaucracy is not taking advantage of recent technological advances, a committee of the National Research Council said yesterday. Over the past several years, DOE has spent between $5.6 billion and $7.2 billion a year on environmental management. But the DOE division responsible for developing innovative cleanup technologies has had its budget slashed from $82.1 million in 1994 to $14.7 million last year, rising slightly to $25 million this year. DOE, which commissioned the report, said it agreed with the findings.