Two federal agencies launched investigations yesterday into evidence that government scientists had submitted phony data to help prove that...

Two federal agencies launched investigations yesterday into evidence that government scientists had submitted phony data to help prove that a proposed nuclear dump at Yucca Mountain in Nevada would be safe.

The disclosure could delay the long-troubled project and undermine assurances that the waste dump would pose no harm for thousands of years. But Energy Department officials cautioned that even if some data were falsified, it would not necessarily discredit all of the research.

Energy Department lawyers discovered a series of e-mail exchanges between scientists that discussed fabricating documentation for a key scientific study about ground-water penetration into Yucca Mountain.

The study was conducted by the U.S. Geological Survey, a part of the Interior Department. It concluded the deep tunnels intended to hold radioactive waste in Yucca Mountain would remain dry for thousands of years, and that radiation could not quickly leak into the ground water.

That scientific question is one of the most critical surrounding Yucca Mountain, a complex engineering project that is running 14 years behind schedule and could end up costing $100 billion. The mountain is supposed to safely isolate radioactive materials for hundreds of thousands of years.

Energy and Interior Department officials said they had launched investigations into the allegedly fabricated data.

Nonetheless, the disclosure inflamed opponents in Nevada, who say the government rigged its research to get the dump licensed as soon as possible

“This proves once again that DOE must cheat and lie in order to make Yucca Mountain look safe,” said Senate Minority Leader Harry Reid, D-Nev. “We aren’t just talking about false documentation on paper. This is about the health and safety of Nevadans and the American people. It is abundantly clear that there is no such thing as ‘sound science’ at Yucca Mountain.”

The project is opposed by Republican and Democratic officials in Nevada. Nevada has won a series of political and legal victories against the project, setting it back years and raising doubts whether it will ever be built.

Bob Loux, executive director of the Nevada Office for Nuclear Projects, said the apparent falsification of data raises grave doubts about the safety of site and, at the very least, will force the Energy Department to replicate years of research to show that rain water does not rapidly flow through fissures in the mountain.

The Energy Department has done two studies of water penetration at Yucca Mountain.

The first was conducted by scientists at Los Alamos National Laboratory, who concluded that water moves through fissures in the mountain far more quickly than the hundreds of years previously thought. The study found rain water had penetrated the rock in just decades.

After the Los Alamos study, the Energy Department contracted with the USGS, which backed up the department’s contention that water migrated very slowly through the volcanic rock. As a result, Energy officials concluded that special alloy casks containing high-level nuclear waste would not corrode for at least 10,000 years, and that any leakage would not be flushed into the ground-water table.