Federal spending cuts will slow down the cleanup of radioactive waste at the Hanford Nuclear Reservation, Washington Gov. Jay Inslee said.

The nation's largest environmental cleanup project is being carried out at the site of the largest U.S. plutonium production plant, which produced plutonium for the nation's nuclear weapons arsenal from World War II until most of its reactors were shut down between 1964 and 1971.

Inslee visited the site in south-central Washington, where six newly leaking tanks of radioactive waste were recently confirmed.

The visit came as federal officials warned of layoffs from budget cuts affecting the Department of Energy.

"I'm very disturbed that at the very month that we have six new leaking tanks of radioactive material, the sequestration hits, which could result in the furlough of several thousand people," Inslee told The New York Times.

As many as 4,800 workers out of Hanford's 9,000-member cleanup work force, mostly employed by private contractors, could face layoffs beginning April 1, Department of Energy officials said.

Of about 56 million gallons' worth of radioactive waste created during Hanford's working lifetime, around 1 million gallons is believed to have leaked over time from storage tanks at the 586-square-mile site, necessitating the giant cleanup effort.

Inslee said the reduction in federal spending will "slow down this process, which we have been waiting decades to get done," and will make the cleanup more expensive for taxpayers in the long run.