-- Los Alamos National Laboratory's next director must do a better job telling the public about the lab's failures as well as its successes, outgoing director John Browne said.

Browne, 60, has resigned, effective Monday, amid a growing number of government investigations into charges of widespread theft and fraud at the nuclear weapons lab.

Browne, a physicist, said last week he was not pressured to quit by federal officials or the University of California, which runs the lab for the Energy Department.

Browne said university President Richard Atkinson told him during a Dec. 23 conversation the lab may need a "management change" to address its problems.

Browne's contract ran through November. He told Atkinson he was prepared to offer his resignation and Atkinson said he would accept it. Also stepping down is Joseph Salgado, a principal deputy director at the lab.

In an interview, Browne said he felt his credibility had suffered too much for him to guide the lab through the latest problems.

"The controversy was so strong and so critical of management that I personally thought the best thing for me to do was resign, and to have the university come in and take it to the next level of performance," he said.

The Energy Department, the FBI and at least two congressional committees are investigating allegations of credit card abuses at the lab over the past several years and the disappearance of high-tech equipment.

In a Dec. 24 letter to Atkinson, Energy Secretary Spencer Abraham also criticized the University of California's management role. "Taken together, these problems have called into question the University of California's ability to run" the Los Alamos lab, he wrote.

Browne said he hopes the interim director -- retired Navy Vice Adm. George Nanos -- will continue efforts started under Browne's administration to improve lab management, including its purchasing and procurement systems.

"What the laboratory has to learn to do better and better is to communicate with everyone, and it's something the new administration at Los Alamos will have to maintain a focus on very strongly," Browne said.

He urged the interim administration to move quickly on improvements and not wait until the university selects a permanent director.

Browne called the job the toughest professional challenge of his life. He said he felt he had made significant improvements, but the controversies had distracted him from improving lab management.

"My tenure as director has felt like sailing a sailboat and trying to put up a new set of sails in the middle of a squall," he said.

The lab, during Browne's tenure, was also tarnished by security scandals that included missing computer disks and the controversy involving former scientist Wen Ho Lee. Lee was jailed for nine months after being accused of stealing nuclear secrets. He denied any wrongdoing and ended up pleading guilty to one a single felony count after the government's case crumbled.

Browne's resignation comes less than two months after Los Alamos released the results of an audit into its credit card program over nearly four years that questioned $4.9 million in transactions.

The lab has said only $2,800 of the total was identified as being used for illegal buys. Watchdog groups say the figure should be higher.

Also, two lab investigators went public with allegations of wrongdoing when they were fired in November. Glenn Walp and Steven Doran were hired last year to investigate the lab's handling of government property and money.