The memo is backed up by little-noticed language in the defense authorization bill that Congress approved this week. The bill suggests that the U.S. nuclear weapons laboratories Lawrence Livermore, Los Alamos and Sandia should be ready to resume testing with as little as six months' notice.

Daryl Kimball, the executive director of the Arms Control Association, said the memorandum demonstrates the Bush administration's intention to end the testing moratorium.

"The administration is chipping away at the barriers to a resumption of testing," said Kimball. "They are doing their best to establish a rationale to resume testing, either for reliability problems or for new weapons. The reality is that there is no scientific nor military basis for a resumption of testing, and to do so would be an enormous strategic blunder that would invite a wave of proliferation that could swamp the entire non-proliferation regime."

New testing could prompt the Russians, the Chinese, Indians and Pakistanis to do likewise, harden North Korea's refusal to abandon its nuclear program and encourage aspiring nuclear powers to accelerate their own weapons programs, he warned.