Washington -- Congressional investigators charged Tuesday that the Lawrence Livermore National Laboratory, one of the country's most sensitive nuclear facilities, can no longer adequately protect weapons materials from potential terrorist threats and is moving too slowly to increase security.

Now an independent watchdog group says the lab should not be permitted to maintain stores of the weapons-grade plutonium, uranium and other radioactive materials at the heart of nuclear warheads.

Testifying before the House Government Reform Subcommittee, the group argued that with the lab in the midst of rapidly growing, heavily populated suburbs, the radioactive materials present too much of a risk to the community and cannot be protected properly.

Officials from the Department of Energy, which owns the lab, rejected many of the criticisms of Livermore and other weapons facilities, arguing that security was being improved rapidly and that they have been sharply increasing spending to provide protection against possible terrorist attacks.

Even as critics called for the lab to relinquish its radioactive materials, the Department of Energy held a public hearing Tuesday in Livermore to outline a proposed 10-year expansion of the lab's nuclear weapons research functions.

Lab spokesman Tom Grim said the plan would roughly double, from 700 to 1, 500 kilograms, the amount of plutonium stored at the lab. Lab scientists and technicians also would research new methods of forming the so-called plutonium "pit," the billiard-ball-size fissionable component of a nuclear bomb.

The hearing drew more than 100 people, many of whom denounced the proposal as a threat to the surrounding communities and to the environment.

"I really am beginning to believe that the government is not friendly to the people," one speaker, Annie Griffin, told lab officials.

Responding to the critics in Washington, Rep. Ellen Tauscher, D-Walnut Creek -- whose district includes the lab and who has been a critic of its security in the past -- flew to Livermore's defense.

"I'm not going to tell you security is perfect, but, because of criticisms, they have made dramatic improvements and have invested sizable amounts of money to increase security," she said in an interview. "In a perfect world, there will be plutonium at Livermore."

The General Accounting Office, the investigative arm of Congress, released a report Tuesday that strongly criticized the Department of Energy for being too slow after Sept. 11 to improve security at Livermore and four other weapons facilities and for setting unrealistic goals for improvements.

The report said the guards at the sites were overworked and poorly trained; the Energy Department was resisting intelligence community assessments of what kind of terrorist attacks it had to defend against; and the department was likely to miss its own deadline for improving some security measures by three years.

Although the report, 2 1/2 years in the making, discussed security lapses at five nuclear facilities, many of its conclusions fell squarely on Livermore and the special problems it confronts.

When the lab, owned by the Department of Energy but managed by the University of California, was founded in the early 1950s to design a new generation of nuclear warheads, it was surrounded by ranches with few inhabitants nearby. Today it is in the middle of a thriving suburban enclave in Alameda County.

In fact, the extremely sensitive Superblock building, where the most important weapons-grade materials are kept, is only about a quarter-mile from some homes, according to the Project on Government Oversight, a private watchdog group.

Danielle Brian, director of the group, told the House subcommittee that the site is simply no longer compatible with certain kinds of weapons research because of the suburban encroachment.

"We can say that the encroaching residential community surrounding Lawrence Livermore has made it nearly impossible to properly protect the weapons quantities of plutonium and highly enriched uranium stored there,'' Brian testified.

"Clearly, (Livermore) will not be able to comply with the new directives, '' tougher security requirements that will be in place by 2006, Brian added.

She suggested that all the nuclear materials at Livermore be moved to the Nevada Test Site, which is 65 miles from Las Vegas and was the site of government underground nuclear testing until a ban was put in place in 1992.

Livermore officials have said the lab could continue to fulfill its primary mission, testing and maintaining the reliability of the current stockpile of nuclear weapons, even if the materials were moved, but it would be more expensive and difficult.

That is why some have raised concerns that moving the materials out of Livermore -- which houses about 880 pounds of plutonium, according to a lab official -- would result in changes in its historic mission and possibly a reduction in its size, something the lab and the Department of Energy would fight.

Linton Brooks, head of the National Nuclear Security Administration, which oversees all weapons work, rejected Brian's charges.

"It is not correct that the physical security challenge at the Lawrence Livermore National Laboratory resulting from residential encroachment makes adequate protection nearly impossible,'' he told the House subcommittee.

Brooks said Livermore's security preparations were tested in February and were ruled satisfactory.

"People looking for soft spots would be ill-advised to come to sites for which I am responsible because they are not soft spots,'' he said.

Tauscher said that the lab was essential to the local economy and that, though security had to improve, it needed to maintain the stocks of bomb materials to conduct its work.

"It's always smarter to consolidate materials in fewer sites to protect them,'' she said after the hearing. "But in order for Lawrence Livermore to fulfill its mission, it has to have some material.''

Tauscher stressed that security has been increased since the Sept. 11 attacks and "remains at its highest level ever.'' She also called on Congress to fund the department's security plan so improvements can continue.

The critical report comes as the Energy Department is preparing to open to competition for the first time the management responsibilities at Los Alamos and Lawrence Livermore labs. Both labs have been run by the University of California, but their management contracts will be up for bid for the first time in the next few years.

Rep. Christopher Shays, R-Conn., chairman of the House subcommittee, didn't single out any of the five DOE sites with supplies of plutonium or enriched uranium, but he made it clear at the hearing that he felt the lab system is overstretched.

"I believe we have too many sites. They are so antiquated they pose a risk,'' he said.

Shays said that taking two years to revise the security plan, which is what the DOE envisions, is "an inexplicably and inexcusably long time.''

Experts have raised concerns in the past that a band of well-armed terrorists might try and break into a weapons facility to steal material to make a nuclear bomb, or might even assemble a bomb at the site and detonate it there.

The current DOE timetable calls for dealing with an attack on Livermore by a small group of terrorists who might want to steal nuclear material, disperse radioactive material, use a truck bomb to attack a lab or set off what's called an improvised nuclear device. It envisions having the new security mechanisms in place by the end of fiscal 2006.

However, U.S. intelligence agencies believe that the DOE faces a potential threat from a larger and better armed terrorist group, requiring even more stringent defensive measures.

Brooks stressed that the future plans go beyond traditional security measures.

"While I am pleased with the progress we have made, our long-term security must be based on more than guns, gates and guards,'' Brooks said. "Over the long term, we are committed to harnessing the power of technology to improve security.''

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Lab security
A GAO report on security at the nation's nuclear weapons labs, including Livermore, found that:

-- Personnel: The Department of Energy has heightened security readiness at the labs, but the increased effort has led to fatigue, turnover and less training for security officers at many sites.

-- Delays: The development of new security plans took almost two years because of bureaucratic delays, and the 2006 target date for completion may not be realistic.

-- Attacks: The security measures fail to contemplate a large-scale terrorist attack.