An investigation of contractors accused of altering medical records and covering up worker exposure to toxic vapors at the Hanford Nuclear Reservation has found no evidence of criminal misconduct, the Energy Department's inspector general said Wednesday.

But a separate report on Hanford by the department's office of independent oversight has found "significant vulnerabilities" in efforts by CH2M Hill, a major contractor on the site, to protect workers from exposure to dangerous chemical vapors.

Taken together, the federal investigations amount to a mixed report card on the behavior of contractors at Hanford, where the state Department of Health is continuing its investigation of alleged irregularities by doctors who cared for injured workers.

Hanford, located beside the Columbia River in eastern Washington, is the nation's largest and most costly cleanup site. Radioactive waste left over from the Cold War production of plutonium is stored there in 177 underground tanks, many of which leak.

It will take three more decades to finish the cleanup there, at a cost of about $2 billion a year.

Energy Secretary Spencer Abraham, who requested both federal investigations in February after worker complaints were reported by a watchdog group and in the media, said he was "pleased" with the findings.

The Government Accountability Project (GAP), the group that first raised questions about the Hanford cleanup in a report last fall, said it was "dismayed" by the inspector general's report and "vindicated" by the office of independent oversight.

The group also expressed concern about the timing of the release of the two reports.

The more positive inspector general's report was released early Wednesday and Abraham's public comments focus on its findings of "no criminal wrongdoing." The much more critical report, which was completed in April but not released until Wednesday, was posted on the department's Web site late in the day.

"The fact that the department is playing games with the release of these reports makes me worry that there is no commitment at the secretary's level for reforming health and safety at Hanford," said Tom Carpenter, director of GAP's Nuclear Oversight Campaign.

Inspector General Gregory H. Friedman said in his report that investigators interviewed more than 70 current and former workers at Hanford, but that "the facts developed during the investigation did not substantiate criminal misconduct."

Perhaps the strongest allegations of misconduct in the GAP report were made against the private health clinic at Hanford, called Hanford Environmental Health Foundation. It alleged that doctors and staff at the clinic altered patient records to misrepresent and minimize vapor injuries to workers who clean up underground tanks.

The inspector general's report did not find evidence supporting these charges.

A number of current and former employees of the clinic, who said they had either falsified medical records themselves or were eyewitnesses to such conduct, gave sworn statements to GAP.

Two former clinic employees told The Washington Post in February that they had been ordered by the medical director at HEHF, Larry Smick, to alter patient records to show that injuries were not related to work on the tank cleanup. Smick, who at the time denied altering any records, was not mentioned in the reports released Wednesday.

The president of HEHF, Lee T. Ashjian, described the inspector general's report as "a vindication" against false charges brought by groups and individuals.

"One can only hope that they will apologize to HEHF now as publicly as they have spoken out against HEHF in the past," Ashjian said.

Under a decision announced before the Energy Department investigations began, HEHF is being replaced this month as the health care provider at Hanford.

The inspector general also cleared CH2M Hill, the contractor in charge of tank cleanup, of allegations of covering up worker exposure to vapors around the tanks.

But the office of oversight report singled out CH2M Hill for "too limited" testing of vapor dangers around the tanks and for work planning and safety controls that are "not sufficiently vigorous."

CH2M Hill did respond to a request for comment on the reports.

Unidentified workers cleaning up radioactive waste at the "tank farms" on the Hanford nuclear reservation in Washington state enter an area known to have hazardous vapors.