Democrats are also pushing an amendment to short-circuit nuclear work in Nevada by transferring $36.6 million for it toward improving conventional "bunker buster" capabilities. Matheson vowed to support that and to seek other opportunities to require congressional approval for any nuclear testing.

Von Hippel refused to name the Defense Department official but said he believes his informant was reflecting high-level opinion in the DOD. He added, "But I think this would be very controversial, and therefore I told him, 'We'll cut you off at the pass.' " That is, opponents would try to thwart new testing.

In another indication of action at the NTS, in April the U.S. Department of Energy released a proposed draft environmental assessment covering "activities using biological simulants and releases of chemicals" there.

It said that after the 9/11 terrorist attacks, the government found a need "for more operational testing, contamination and decontamination testing, forensics testing, personal protective equipment (PPE) testing, enclosed environment detection and decontamination testing and counter-terrorism training as they relate to biological or chemical agents."

The NTS provides a remote, secure setting for such defensive testing, it added. Chemicals in low concentration and harmless biological simulants would be released on the NTS. About five to 20 test series per year would be carried out, and no more than two new employees would be required, it said.

However, defensive research against chemical and biological threats already is carried out on the Army's Dugway Proving Ground, located in the western Utah desert. In 2002, Dugway issued a proposal to substantially increase chemical and biological defenses and counterterrorism training.

Erickson said sometimes simulants can cause illness but that would be a minor problem, unless the exposed person was in compromised health. If simulants were used at the NTS, he does not think dangerous concentrations could reach Utah.

As far as Erickson is concerned, the larger concern is the test site's future.

"What's the public policy decision here?" he asked.

The possibility of resuming tests is "more than talk," he said. "They're funding preparations for it. No decision has been made to proceed with tests."

In addition to funding for nuclear testing, the Bush administration has requested funding to research and develop earth-penetrating nuclear bombs, he said. These bunker-busters are "what they call mini-nukes, or small-yield nuclear weapons."

As part of the newly proposed program, test site officials would like to place caches of simulants in tunnels and blow them up, he added. Instruments would be checked to see whether they could sniff out the underground simulants.

"One of the purposes of the robust nuclear earth penetrator, the bunker buster, is to dig its way down into the earth hundreds of feet before detonation of the nuclear warhead," Erickson said.

Such a weapon could be used to vaporize any chemical or biological weapon stored in an underground bunker, he added.

Daryl Kimball, executive director of the Arms Control Association, based in Washington, D.C., said the Bush administration "has taken some steps that have eroded the legal and technical barriers to the resumption of testing."

The group is dedicated to controlling arms, and von Hippel has contributed to its Web site.

Kimball said a reason for thinking the Bush administration wants to resume testing is that it opposes ratification of the comprehensive test-ban treaty.

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E-mail: bau@desnews.com