By Walter Pincus
Washington Post Staff Writer
Monday, June 12, 2000; Page A02

The Senate has paved the way for the Energy Department's nuclear weapons laboratories to aid Pentagon research into a new low-yield nuclear weapon that could destroy hardened and deeply buried targets by penetrating far into the ground before exploding.

The purpose of the study is to develop "a deep penetrator that could hold at risk a rogue state's deeply buried weapons or Saddam Hussein's bunker without torching Baghdad," said one former senior Pentagon official who is still involved in government military and intelligence research.

The most recent modernization of a U.S. strategic nuclear weapon, the B-61 thermonuclear bomb, took place in the early 1990s. At that time the bomb, which has a variety of yields above 50 kilotons (or 50,000 tons of TNT, more than three times the power of the Hiroshima bomb), was given an earth-penetrating capability great enough to destroy "a garden variety underground bunker, 100 meters into solid rock," the former official said.

"What's needed now is something that can threaten a bunker tunneled under 300 meters of granite without killing the surrounding civilian population," he said.

Last year, a Pentagon effort to get assistance from Energy's weapons labs in researching the options for such a weapon was blocked when Energy lawyers said a 1994 provision in the law prohibited the government's nuclear laboratories from "all research and development which could lead to a precision, low-yield nuclear weapon," according to a senior Energy official who asked not to be identified.

To overcome that roadblock, Senate Republicans this year put a provision in the fiscal 2001 defense authorization bill that specifically requires the secretaries of Defense and Energy to undertake such a study and permits the nuclear labs to "conduct any limited research and development that may be necessary" to complete it, according to a Senate Armed Services Committee report.

The measure is expected to pass the Senate this week and eventually be approved by a House-Senate conference, according to its supporters.

Supporters of this new low-yield nuclear weapon include a small group of senior Republican senators and some top officials within the nuclear weapons community who, in the wake of Senate defeat of the Comprehensive Test Ban Treaty last October, believe the United States may soon need to resume underground testing to design new warheads and maintain old ones.

"The United States will eventually need a new, low-yield nuclear weapon" because the explosive power of silo-busting thermonuclear warheads designed for the Cold War is "too high" to deter small nations in today's multipolar world, said Paul Robinson, the head of Energy's Sandia National Laboratories, one of the nation's leading weapons labs.

Without building such a new weapon, "we would end up being self-deterred," Robinson said at a forum in New Mexico last March.

Sen. Wayne Allard (R-Colo.), chairman of the Senate Armed Services strategic subcommittee, sponsored the defense bill amendment because, as he said at a May 23 committee meeting, the legislative language from 1994 prohibited Energy's nuclear laboratories "from conducting any research related to the design of a new low-yield nuclear warhead."

"I understand the attorneys have blocked the Energy weapons labs from conducting any studies or research to support the Defense Department in assessing options for addressing current or future threats because of this 1994 provision," Allard said.

Armed Services Committee Chairman John W. Warner (R-Va.) said at the May 23 hearing: "I do not believe that, in the foreseeable future, we're going to see the abolishment totally of nuclear weaponry. . . . And, therefore, we've got to maintain a capability in the United States for a future president or presidents to initiate a program, to build a new warhead."

In a recent telephone interview, Warner said, "The next president has got to put this on top of his agenda." He added, "We should do research and analysis" that could lead to new weapons because "there is a dwindling industrial base and dwindling category of capable people to build weapons."

Texas Gov. George W. Bush, the presumptive GOP presidential candidate, who opposed approval of the Comprehensive Test Ban Treaty, has supported a moratorium on testing "because it gives more flexibility," said Condoleezza Rice, Bush's foreign policy adviser and a member of the National Security Council staff during his father's administration.

Bush foresees any resumption of testing in the near future as being based on "questions of reliability and safety" of current weapons, Rice said in a telephone interview. As for developing new weapons, Bush is "reserving judgment. . . . It has not come up, but it is not inconceivable," she said.

Bush, in a May 23 speech, said that "America should rethink the requirements . . . for nuclear deterrence and a new security environment." He said that if elected president, he would get his defense secretary "to conduct an assessment of our nuclear force posture."

The last full Pentagon nuclear posture review was in 1994, with an update in 1997 before the Helsinki summit between President Clinton and Russia's Boris Yeltsin. The current Senate version of the fiscal 2001 defense authorization bill not only permits research on the new low-yield weapons but also calls for the secretary of defense, "in consultation with the Secretary of Energy, to prepare a plan for the long-term sustainment and modernization of U.S. strategic forces."

That nuclear posture study, the panel said, "would look beyond current efforts to modernize existing systems and lay out a comprehensive vision for the maintenance of deterrent forces."