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One tank was already known to have a leak, but the new revelation caught state officials by surprise, said David Postman, a spokesman for the governor. He said that federal managers had assured the governor that the leaks posed no health risks or threats to the water supply, including the Columbia River, which passes nearby.

But Mr. Postman said it was also unclear how long the additional tanks have been leaking. What federal officials called a "data analysis" revealed the problem, Mr. Postman said. Hanford was built in the 1940s for the Manhattan Project, then continued on for decades through the cold war as a manufacturing site for the nuclear arsenal.

The Department of Energy, Mr. Inslee said in a statement, "did not adequately analyze data it had that would have shown the other tanks that are leaking."

Political leaders in Washington State and Oregon were already on high alert about Hanford as new worries about the site's pollutants combined with concerns about federal budgets, especially if automatic spending cuts — the sequestration threat hanging over Congress — kick in, affecting the cleanup budget.

The Department of Energy, which oversees the site, said last week that one of the 177 tanks at the site was leaking radioactive waste liquids at a rate of 150 to 300 gallons per year. The department said then that the tank, which holds approximately 447,000 gallons of sludge, was the first one documented to be losing liquids since interim stabilization of Hanford's tanks was completed in 2005.

Mr. Inslee, who took office last month, said after the first leak was announced that he was "alarmed and deeply concerned."