The Bush administration's fiscal 2004 budget request for the Energy Department's Nuclear Security Administration asks for $21 million for new weapons studies, including $15 million for exploring the feasibility of a robust nuclear earth penetrator and $6 million to set up advance design teams to look at other concepts. A Feb. 20 article incorrectly reported that it included $21 million for the latter program alone. (Published 2/21/03)

The Bush administration is reviving interest in developing low-yield nuclear devices that could be used to destroy targets, such as reinforced bunkers holding chemical or biological weapons, with less damage to the surrounding area than today's giant warheads, according to administration officials and government scientists.

The program is based on views within the nation's nuclear weapons laboratories that as the United States reduces its stockpiles of larger nuclear weapons, it should replace them with smaller numbers of low-yield bombs. Low-yield nuclear weapons have much less explosive power than the large nuclear bombs that comprise today's strategic arsenal. Nuclear weapons strategists believe low-yield weapons would be a more credible deterrent against outlaw states and terrorist organizations with weapons of mass destruction. Since the bombs would inflict much less damage to the area outside the target than high-yield devices, the threshold for using them presumably would be lower.

Low-yield nuclear weapons have been controversial since the late 1970s, when the Army tried to introduce neutron artillery shells and warheads with its forces in Europe. The explosion of the neutron weapon created enormous radiation, while its blast and heat -- though still powerful -- were smaller than traditional nuclear bombs. This made the weapon attractive to military officials planning for a possible war against the Soviet Union in Europe's densely populated areas.

Described as effective at killing people while leaving buildings standing, the neutron weapons were deferred by President Jimmy Carter after a public uproar in Europe and the United States. President Ronald Reagan revived the weapons, but President George H.W. Bush eliminated them as part of an agreement to reduce tactical nuclear weapons overseas.

Discussion of developing low-yield weapons returned in the 1990s when officials studied the possibility of creating high-altitude low-yield weapons to produce an electromagnetic pulse that could wipe out enemy communications and electronics.

The low-yield weapons being considered now would be designed to penetrate reinforced bunkers housing chemical or biological weapons and detonate underground, concentrating their explosive power and heat on the chemical or biological agents and reducing or eliminating radioactive fallout in the atmosphere, scientists say.

Officials from the Defense and Energy departments met at the Pentagon on Jan. 10 to discuss plans for a conference on the future of the U.S. nuclear stockpile, an Energy Department spokesman said. The idea of reviving the low-yield nuclear weapons development program was among the subjects to be discussed at the conference, scheduled for August at the Omaha headquarters of Strategic Command, the Pentagon command responsible for the country's nuclear arsenal.

"Requirements for low-yield weapons," including neutron or enhanced-radiation weapons that create less heat and minimize explosive effects, along with "agent defeat weapons" designed to neutralize chemical and biological weapons, were put on the agenda for a Future Arsenal Panel at that conference, according to notes from the Pentagon planning session. The notes were released this week by the Los Alamos Study Group, a New Mexico-based organization that tracks U.S. nuclear weapons activities.

Defense Secretary Donald H. Rumsfeld was asked about the notes at a Pentagon news conference yesterday. "I don't believe there is anything currently underway by way of developing new nuclear weapons," he said.

He added that the notes "referred not to the development of specific weapons, but the analysis that would go into determining whether or not something might or might not make sense."

The Future Arsenal Panel at the August meeting will discuss computer modeling for possible new nuclear devices and what type of testing, if any, would be needed, the notes say. The notes add that consideration of the new weapons is being prompted by the Nuclear Posture Review completed by the Bush administration last year.

The Nuclear Posture Review called for the reduction by two-thirds of the country's 6,000 operational nuclear warheads and bombs over the next 10 years. It provided for keeping several thousand warheads in a strategic reserve and allowed for the development of new weapons based on changed security requirements.

Under an arms control treaty reached by President Bush and Russian President Vladimir Putin last May, Russia committed itself to wholesale reductions in its strategic nuclear arsenal as well.

One of the most controversial features of the Nuclear Posture Review is that it seemingly left the door open to using nuclear weapons for a preemptive attack on a threatening foreign country. The new study of low-yield nuclear devices would be compatible with that provision.

Another matter before the August conference will be the prospect of resuming nuclear testing, the notes said. The conference also will study the impact of a resumption of testing on public opinion in the United States and abroad.

"They are going to discuss not only weapons and testing policies but the politics to get them approved," said Greg Mello, director of the Los Alamos Study Group. "It's rare that so many details about the nuclear weapons agenda of the Bush administration would appear in one document."

The August conference comes on top of the administration's 2004 budget request, which seeks money to continue refurbishing and modernizing thousands of deployed nuclear warheads. It also calls for study of a "robust earth penetrator," a nuclear device that would destroy buried, hardened underground bunkers for command posts or weapons storage.

The Nuclear Security Administration, which runs the nation's nuclear weapons complex at the Energy Department, is requesting $6.4 billion next year, an increase from this year's $5.9 billion and almost $1 billion above the last budget presented by the Clinton administration. The new request calls for $15 million for the earth penetrator and $21 million for two of the nation's national nuclear weapons laboratories, Los Alamos and Lawrence Livermore, to assemble design teams to study advanced nuclear concepts. The teams are being created so that the United States has the expertise to build new weapons or change existing ones, senior Energy Department officials said.

Last week, a House Republican policy committee recommended that the Pentagon's Nuclear Weapons Council revitalize advanced nuclear weapons development and that Congress consider repealing a 10-year ban on research on low-yield nuclear weapons, those whose explosions are less than 5 kilotons, the explosive equivalent of 5,000 tons of TNT.

"It allows the United States to have teams of scientists and engineers working on emerging threats and potential problems before they become severe," the GOP policy committee report said.

"I don't believe there is anything currently underway by way of developing new nuclear weapons," Defense Secretary Donald H. Rumsfeld said at a news conference.