WASHINGTON - A check of classified documents mailed from Pacific Northwest National Laboratory and two other national labs found 15 percent went to addresses not approved to receive such material.

Department of Energy officials insist the errant mailings, disclosed in a new report from the agency's inspector general, did not compromise security and that the problem has been fixed.

But that assessment was challenged Wednesday by the Senate Intelligence Committee chairman.

"They don't know that," said Sen. Richard Shelby, R-Ala. "You can rationalize, justify just about anything, but at the end of the day, you don't know what might have been lost. You have to fear the worst in a situation like that."

The Energy Department keeps a computer database of addresses that are eligible to receive classified data. Anyone mailing classified data is supposed to check this list to ensure the address is approved.

"We had an approved process through the DOE field office in Richland that we were following," said Greg Koller, spokesman for PNNL. "We don't believe the (inspector general) fully understood the transmittal procedures we have in place for classified documents."

PNNL does classified work for federal agencies other than DOE, such as the Department of Defense, the Central Intelligence Agency and the Department of Justice. People with clearance to receive classified documents at that agency are not always registered in DOE's computer database, Koller said.

"PNNL works with DOE in identifying the folks the documents need to go to and even though they are not on the database, they were known, authorized recipients as identified in concert with DOE," said Mike Talbot, a spokesman for the Richland DOE office.

Classified addresses are verified and reverified before documents are sent, and return receipts are required to confirm there was no tampering detected with the materials, Koller said.

The investigation examined 177 mailings of classified documents last year from the Los Alamos Nuclear Weapons Laboratory, the Lawrence Livermore National Laboratory in Livermore, Calif., and PNNL.

Investigators found that 27 of the mailings, or about 15 percent of those reviewed, were sent to other federal agencies or federal contractors that were not in the database of approved addresses. Three of the mailings were from the Richland lab.

The report said the mailings to unauthorized addresses were discovered in May, shortly after two computer disks containing nuclear secrets disappeared from the Los Alamos National Laboratory in New Mexico. The disks reappeared three months later behind a copying machine at the lab.

Department security officials alerted by the agency's inspector general acknowledged the mailings violated department policy but concluded no classified information was compromised. They blamed contractors who did not have access to the list of approved addresses.

But Inspector General Gregory H. Friedman disagreed. In his report to Energy Secretary Bill Richardson, he blamed a "breakdown in the execution of internal controls designed to prevent transmittal of classified documents to inappropriate recipients."

Richardson's spokesman said agencies involved have recommended ways to correct the shortcomings. "I'm confident that General Gordon ... will work to ensure the fixes are made so the problems and errors are not repeated," said spokesman Stu Nagurka. Air Force Gen. John Gordon heads the National Nuclear Security Administration, created by Congress last year to oversee the labs.