WASHINGTON -- The Bush administration issued a report Friday backing the scientific data behind Yucca Mountain, almost a year after the Energy Department disclosed that government scientists might have fabricated their work on the project.

Paul Golan, acting director of the department's Office of Civilian Radioactive Waste Management, said an internal examination found the science at Yucca Mountain to be "strong" and "valid."

But the computer work relating to water and climate studies failed to meet department standards and is being redone by the Sandia National Laboratories, he said.

"Despite the fact that the science is consistent, our quality assurance requirements were not met, which is a requirement for submitting a license application to the Nuclear Regulatory Commission," Golan said. "We find it best to just replace this work."

In March, the Energy and Interior departments revealed that several U.S. Geological Survey hydrologists had exchanged e-mails discussing possible falsification of quality assurance documents on water infiltration research.

The e-mails -- written between May 18, 1998, and March 20, 2000 -- by two to three USGS scientists said that dates and names on the project had been made up and that "fudge factors" were used to meet quality assurance requirements.

The disclosure led to the launching of several investigations by the Department of Energy and audits by the inspectors general of the Interior and Energy departments.

It was a setback for an already delayed program undergoing a redesign for new canisters that government scientists said would better hold nuclear waste in the mountain 100 miles northwest of Las Vegas.

In their probe, Energy Department investigators sampled more than 10 million e-mails, expanding their search to messages through 2004, according to the 144-page report.

The report concluded that the science used to determine the ranges of rainfall seepage into Yucca Mountain mirrored that of similar water studies by other scientists in the region. Water at the site eventually could corrode the waste canisters and potentially spread radiation to sources of drinking water, critics say.

Ultimately, the 2002 decision by then-Energy Secretary Spencer Abraham to recommend Yucca Mountain as a permanent repository for 77,000 tons of spent fuel rested on sound science, investigators found.

Nevada Nuclear Projects Agency chief Bob Loux questioned the credibility of an internal report. "I don't think it's any secret that DOE has not been objective in their investigation of Yucca Mountain," Loux said. "The science itself has always been questioned."

Nevada lawmakers said administration officials have failed to address the root problems of the project, which now lacks a timetable or cost estimate.

"The DOE, which failed to prevent the falsification of scientific data on Yucca Mountain projects in the first place, now wants to us to believe that the falsifications made no difference in the quality of the work. That's absurd," Sen. Harry Reid, D-Nev., said in a prepared statement.

Sen. John Ensign, R-Nev., said the report was a "misguided attempt by the DOE to gloss over mismanagement and incompetence."

At a nuclear power industry conference earlier this week, Energy Secretary Samuel Bodman acknowledged problems with the work USGS scientists had done at Yucca.

Golan said the violations rested in the Quality Assurance program, a protocol requiring scientists and engineers to record and document their research, computer modeling and field reports so that they can be verified and confirmed as part of repository safety licensing.

Scientists at the Department of Energy's Sandia laboratories have been recoding the data since September, Golan said. The review is expected to take several more months, and independent experts also will check the work. "It's very important we go about this in a deliberate way," Golan said.

Golan estimated that the recoding would cost taxpayers between several hundred thousand dollars to several million dollars. He declined to say how long the e-mail investigation has held up the project or when the government would submit its license application to the Nuclear Regulatory Agency.

Rep. Jon Porter, R-Nev., chairman of the Federal Workforce and Agency Organization Subcommittee, said his panel's investigation has found evidence of a "severely flawed quality assurance process."

And he has subpoenaed the Energy Department to hand over its 5,000-page draft license application for Yucca Mountain, which critics say would shed more light on the department's research. The department has not complied.

Golan said the department is conducting a separate investigation into its quality assurance program, which critics for years have questioned.

Investigators are reviewing thousands more e-mails and employee complaints in response to a November audit by the department's inspector general. The complaints claimed that the investigation into the USGS e-mails was too narrow.

Rep. Jim Gibbons, R-Nev., said the Department of Energy should redo its scientific work. "The e-mails sent between federal workers indicated disturbing flaws and pressure to make their science match a desired outcome, namely proving the safety of Yucca Mountain," he said. "Today's report in no way addresses this apparent breach of scientific integrity."

Rep. Shelley Berkley, D-Nev., said the report "does not close the book on the inexcusable behavior of USGS employees who admitted in their own e-mails that they cut corners, faked their work and broke the rules."

The Interior Department is investigating the conduct of the employees.