In substantial retreat from the president's first-term policies, Bush administration officials say they have given up pursuing entirely new nuclear weapons for at least the immediate future, saying support isn't strong enough in Congress and the military.

Weapons authorities in the government and its three weapons design labs in New Mexico and California still hope for a fresh era of inventing new H-bombs and warheads.

But despite report after report from the Bush administration arguing the need for such new weapons, federal and lab officials say no clear political momentum has developed.

Instead, prompted by a powerful Republican appropriations chairman, they're pushing the idea of designing replacements for the 1970s and'80s vintage weapons in the current U.S. arsenal, without ever conducting a full explosive nuclear test.

Along the way, weapons officials acknowledge, the redesigns could deliver some of the new or improved capabilities that the administration wants, such as low-yield weapons and earth penetrators, an outcome that one senior federal weapons executive calls "fortuitous."

Unlike their counterparts in the Soviet Union, U.S. scientists crafted Cold War bombs and warheads to deliver the greatest explosive power for the least size and weight, to pack as many as possible into the nose of missiles. Making such "highly optimized" weapons demanded exotic, expensive materials and methods of manufacture, some difficult to replicate under current environmental regulations.

According to federal and lab weapons officials, a new Reliable Replacement Warhead program endorsed by Congress in November would revamp today's weapons, making them less efficient but more resistant to aging and less expensive to make.

Arms-control and disarmament advocates are wary that the new weapons-design program is a pretext for devising the kinds of wholly new bombs and warheads repeatedly sought in administration policy statements and internal advisory reports. The administration is strongly pushing for building a new weapons factory to make the plutonium fission cores at the heart of every H-bomb, and not solely for the existing arsenal but for any future design.

"It sounds like an attempt to dress up a new weapons program in nice clothing," said Daryl Kimball, executive director of the Washington-based Arms Control Association. "I'm skeptical about their intentions and where this program could be 10 or 15 years from now."

Everet Beckner, deputy chief of weapons for the U.S. Department of Energy's National Nuclear Security Administration, said Congress appears solidly behind the ideas that the United States should be "a nuclear power second to none" and needs a "sizable" nuclear arsenal.

"The consensus falls apart when you ask what that means," Beckner said in a recent interview. "Does it mean you make changes? Does it mean you add things?"

The administration's Nuclear Posture Review called in December 2001 for low-yield nuclear weapons, for nuclear earth penetrators, for nuclear "agent defeat" weapons to destroy chemical and biological munitions and possibly other weapons designs tailored for a specific blend of radiation, blast and heat.

For two years, Congress went along. Lawmakers scrapped a 10-year-old prohibition on researching low-yield weapons and approved funds for exploring new weapons designs.

But faced with resistance from Democrats and Ohio Republican David Hobson, chair-man of the House Energy and Water appropriations committee, administration officials realized they didn't have solid voting majorities for entirely new classes of nuclear weapons, especially those that might require nuclear testing to prove the designs before manufacturing and fielding.

In contrast to the Nuclear Posture Review and recommendations of the Defense Science Board as recently as February 2004, NNSA chief Linton Brooks told a Senate armed services subcommittee Monday that U.S. nuclear-weapons scientists are not designing for new military capabilities. Rather he made a pitch for future weapons-manufacturing infrastructure and for the one weapon that the administration still is seeking, the modification of an existing H-bomb that would encase its thermonuclear explosive in a heavier, more rugged case to pierce rock and attack underground targets.

Rather than produce new weapons that would require nuclear testing, Brooks and Beckner say the reliable warhead program should stave off the need for nuclear tests.

Contact Ian Hoffman at ihoffman@angnewspapers.com.