Thomas P. D'Agostino, head of defense programs for the National Nuclear Security Administration (NNSA), said on Thursday that the "Complex 2030" program would repair or replace "inefficient, old and expensive (to maintain)" facilities at eight sites, including some buildings going back to the 1940s Manhattan Project that built the first atomic bombs.

The sites, primarily in California, New Mexico, Texas and Tennessee, "are not sustainable for the long term," a report published by The Washington Post on Friday quoted D'Agostino as saying.

The announcement came as U.S. President George W. Bush was pressing its allies to take harsh steps to halt nuclear weapons programs in both the Democratic People's Republic of Korea and Iran that it said were violations of the nuclear Non-Proliferation Treaty. That same treaty called for the United States and other members of the nuclear club to eliminate their own stockpiles, but it gave no deadline by which that should take place.

The Bush administration's plan would replace the aging Cold War stockpile of about 6,000 warheads with a smaller, more reliable arsenal that would last for decades. It would also consolidate the handling of plutonium, the most dangerous of the nuclear materials, in one center that would be built at a site that already houses similar special materials. Another part of the plan would be to remove all highly enriched uranium from the Lawrence Livermore National Laboratory in California, D'Agostino said.

Key to the Bush plan was an expected decision in December by the NNSA on a design for the new "Reliable Replacement Warhead" (RRW). The nation's two nuclear weapons laboratories, Los Alamos and Lawrence Livermore, are competing for the new warhead design.

Before going ahead with any new warhead, however, the NNSA would have to get Congress's approval to move into actual engineering development.

A requirement of the new design was that it must be based on nuclear packages tested in the past so that it would not require the United States to break the moratorium on underground tests to make certain the RRW would work, the report said.

The process initiated Thursday would provide the public the first chance to give its views on the Bush nuclear program. To carry out the rebuilding of the complex, the agency must prepare updated environmental-impact statements for the eight sites, including public comments, and hold hearings at each location, the report said.