Federal security officials and computer experts have been sent to Los Alamos National Laboratory to ensure directives at the nation's premier nuclear weapons lab are being followed in the wake of a possible security breach.

The FBI was called in last week after police in northern New Mexico stumbled onto what appeared to be classified information from the lab while arresting a man at a mobile home for possession of drug paraphrenalia.

The information was discovered on computer during a search for evidence of a drug business, said Los Alamos Police Sgt. Chuck Ney. He said police alerted the FBI to the documents, which appeared to contain classified material.

The mobile home's owner, who wasn't home at the time, was listed as a former employee of one of the lab's subcontractors.

Linton Brooks, head of the Energy Department's National Nuclear Security Administration, said Wednesday he was sending NNSA's chief of defense nuclear security to investigate, along with a team of computer specialists to ensure compliance with department directives at the lab.

He said investigators want to find out how the latest possible security breach could occur despite "extraordinary efforts in the last three years to put strong security procedures in place" at Los Alamos and other weapons facilities.

Los Alamos has a history of high-profile problems that have highlighted sloppy inventory control and security failures at the nuclear weapons lab.

In 2000, nuclear scientist Wen Ho Lee pleaded guilty to one count of mishandling computer files. In 2004, the lab was temporarily shut down after two computer disks were reported missing; it turned out they never existed and it was an inventory error. The lab was put under new management and the Energy Department began moving toward creating a diskless environment to prevent classified material from being carried out.

"We intend to do everything possible to guard against any criminal activity, particularly where a breach of security may be involved," Lab Director Michael Anastasio said.

Gov. Bill Richardson, a former energy secretary in the Clinton administration, noted the lab had made efforts to improve security but apparently not enough.

"We need to plug the leaks, we need to beef up security," the governor said Wednesday. "This can't keep happening."

FBI spokesman Bill Elwell in Albuquerque said the investigation is continuing and that he couldn't talk about the evidence seized from the home or the individuals connected to the case.

The woman who owned the mobile home had worked for lab subcontractor Information Assets Management until about two weeks ago. A spokeswoman at Information Assets Management would say only that the woman "is not currently employed with us." The company helps organizations shift from paper-based files to electronic systems.

The federal charge of unauthorized removal and retention of classified material is a misdemeanor that carries a maximum sentence of a year in prison and up to a $100,000 fine.