A House committee is expanding its inquiry into allegations of fraud and credit card abuse at Los Alamos National Laboratory. A letter from the committee said abuse appears more widespread than originally suspected.

The committee asked for new documents, including reports on the alleged irregularities submitted to Director John C. Browne and on whether the computers missing from the nuclear lab contained classified information.

Ken Johnson, spokesman for the House Energy and Commerce Committee, said three investigators are being sent to the lab and will begin work Monday.

"It is apparent that the amount of fraud and abuse at LANL is much more extensive and includes many more employees than we had originally . . . believed," said the letter, signed by Chairman W.J. "Billy" Tauzin (R-La.) and other senior committee members.

The letter to Richard C. Atkinson, president of the University of California, which runs the lab, expressed frustration with "the apparent failure of the University of California and LANL to sufficiently address these issues over the past several years."

The letter, sent Tuesday and distributed yesterday, requested documents regarding the firing of two investigators who had blown the whistle on the lab's management practices. It also demanded materials from PricewaterhouseCoopers, the lab's auditor.

Johnson said the expanded request for documents was a result of questions raised by papers received after an earlier committee request, by news reports and by information from Los Alamos employees "suggesting that the problems are more prevalent than first reported."

Danielle Brian, executive director of the Washington-based watchdog group Project on Government Oversight, which has worked with Los Alamos whistle-blowers, said the letter is an encouraging sign.

"We think it's a great start. It's obviously a serious investigation," she said.