Despite a cleanup effort expected to cost tens of billions of dollars, some badly contaminated nuclear weapons plant sites probably will never be returned to their natural state, an outgoing Energy Department official says.

In an interview with United Press International, Joseph Salgado, whose tenure as deputy energy secretary ended Friday, also said there remains "deep-seated institutional resistance" within the department's weapons complex to new safety and environmental initiatives he spearheaded for former Energy Secretary John Herrington.However, Salgado said the internal opposition is melting under intense media and congressional scrutiny and public pressures generated by the past year's revelations about dangerously aging reactors and massive radioactive and toxic pollution at 17 weapons plants in 12 states.