Craig Lawrence, an assistant U.S. attorney, told U.S. District Judge Royce C. Lamberth yesterday the computer storage drives of former EPA administrator Carol M. Browner and a top aide were erased by a contractor just before Clinton left office on Jan. 20.

"We take this matter very seriously," Lawrence said. "That's why we walked into court today and gave him as much information as we have."

Lamberth ordered the EPA on Jan. 19 to preserve all records relating to a lawsuit filed by the Landmark Legal Foundation last fall. The lawsuit, filed under the Freedom of Information Act, seeks documents relating to the involvement of outside groups in regulatory actions the EPA took in the final months of the administration.

"It's very, very serious when evidence that is the subject of litigation is tampered with," said Mark Levin, president of the foundation, which brought the suit.

In addition to the hard drives erased on Jan. 19, Lawrence said the contractor removed material from computers of two other Clinton EPA officials on Jan. 26. The drives apparently were erased as part of the process of moving from one administration to another, according to government lawyers.

After the government's disclosure, Lamberth granted the foundation's request to question Browner under oath about the information sought in the lawsuit. Officials said Browner ordered that her computer drive be erased before she left office, but government lawyers said they believe the erasure of her hard drive occurred before Lamberth's order was signed -- although they apparently occurred on the same day.

Government lawyers said they are investigating whether they can recover any lost material from backup tapes.