Energy Secretary Steven Chu says cuts set to start taking effect Friday would delay work at the Energy Department's highest-risk sites.
That includes the Hanford Nuclear Reservation in Washington state, the nation's most contaminated nuclear site, where six tanks are leaking radioactive waste left over from decades of plutonium production for nuclear weapons.
Other high-risk sites facing work delays are in Tennessee, South Carolina and Idaho.
The Energy Department is facing an estimated $1.9 billion in spending cuts, including $900 million for the National Nuclear Security Administration. That agency is responsible for maintaining and securing the nation's nuclear weapons stockpile.
Meanwhile, Hanford officials are considering a number of options to deal with six leaking waste tanks there, including covers over the tanks to prevent rainfall from getting into them, a state official told lawmakers Thursday.
Two such covers already have been installed over tank farms at the Hanford nuclear reservation, and they have remarkably decreased the amount of moisture around the tanks, according to Jane Hedges of the Washington state Department of Ecology.
In the meantime, Hedges said, state and federal officials are still evaluating their options for controlling the leaks.
The federal government created Hanford in the 1940s as part of the top-secret Manhattan Project to build the atomic bomb.
Today, the most vexing task in a cleanup that's expected to last decades is the removal of millions of gallons of highly radioactive waste from 177 aging, underground tanks, many of which are known to have leaked in the past. Workers have since removed all liquids that could be pumped out from the tanks and reported that as stabilized in 2005.
But last week, state and federal officials announced that six tanks are now leaking. The tanks hold a toxic and radioactive stew of waste left from decades of plutonium production for U.S. nuclear weapons.
Hedges testified before a work session of the state Senate Energy, Environment and Telecommunications Committee. Under questioning from committee members, he stressed that the leaks pose no immediate threat to public safety or the environment.
The tanks sit several feet above the groundwater table, and it would take decades for the waste to reach it, she said. In addition, four of the six tanks in question sit 8 miles from the Columbia River, while the remaining two tanks sit 5 miles from the river.
"There is no risk to our agriculture community, to irrigated farmland, no risk to the river, the people in the Tri-Cities who get their drinking water from the river," she said.
Washington Gov. Jay Inslee and Oregon Gov. John Kitzhaber have called for additional tanks to be installed to transfer waste out of leaking tanks.
The cost for one, double-walled tank is estimated at between $150 million and $500 million, Hedges said.
The federal government already spends about $2 billion each year on Hanford cleanup - one-third of its entire budget for nuclear cleanup nationally.