Washington - Defense Secretary Robert M. Gates said Tuesday that the United States would hold "fully accountable" any country or group that helped terrorists to acquire or use nuclear, chemical or biological weapons.
The statement was the Bush administration's most expansive yet in attempting to articulate a vision of deterrence for the post-Sept. 11 world. It went beyond the cold war notion that a president could respond with overwhelming force against a country that directly attacked the United States or its allies with unconventional weapons.
"Today we also make clear that the United States will hold any state, terrorist group or other nonstate actor or individual fully accountable for supporting or enabling terrorist efforts to obtain or use weapons of mass destruction - whether by facilitating, financing or providing expertise or safe haven for such efforts," Mr. Gates said.
The comments came in an address in which he said it was important to modernize the nation's nuclear arsenal as a hedge against what he described as "rising and resurgent powers" like Russia or China, as well as "rogue nations" like Iran or North Korea and international terrorists.
By declaring that those who facilitated a terrorist attack would be held "fully accountable," Mr. Gates left the door open to diplomatic and economic responses as well as military ones. And, to be sure, the United States has acted forcefully before against those who sheltered terrorists, with the invasion of Afghanistan to oust Al Qaeda and its Taliban government supporters after the attacks of Sept. 11.
His speech here before the Carnegie Endowment for International Peace was the latest signal that the administration was moving in its closing months to embrace more far-reaching notions of deterrence and self-defense.
On Monday, senior officials justified a weekend attack against a suspected Iraqi insurgent leader in Syria by saying the administration was operating under an expansive new definition of self-defense. The policy, officials said, provided a rationale for conventional strikes on militant targets in a sovereign nation without its consent - if that nation were unable or unwilling to halt the threat on its own.
By law, the new president must conduct a review of the nation's nuclear posture, and Mr. Gates's address could be viewed as advocating a specific agenda for the next occupant of the White House.
The first public indication that the administration was expanding the traditional view of nuclear deterrence came in a statement by President Bush in October 2006 that followed a test detonation of a nuclear device by North Korea. Mr. Bush said North Korea would be held "fully accountable" for the transfer of nuclear weapons or materials to any nation or terrorist organization.
The president was not as explicit then as Mr. Gates was on Tuesday in saying that the administration would extend the threat of reprisals for the transfer of nuclear weapons or materials to all countries, not just North Korea. Mr. Gates also expanded the threat to nations or groups that provide a broader range of support to terrorists.
Early this year, in a little-noticed speech at Stanford University, Stephen J. Hadley, Mr. Bush's national security adviser, also spoke of how the president had approved an expanded deterrence policy.
In his speech Tuesday, Mr. Gates argued for modernizing the nation's nuclear arsenal because "as long as other states have or seek nuclear weapons - and potentially can threaten us, our allies and friends - then we must have a deterrent capacity."
Although Mr. Gates earlier this year fired the Air Force secretary and chief of staff after the discovery of shortcomings in the service's stewardship of nuclear weapons and components, he stressed that the nuclear arsenal was "safe, secure and reliable."
"The problem is the long-term prognosis - which I would characterize as bleak," he said.
Veteran weapons designers and technicians are retiring, and Congress has not voted for the money to build replacement warheads for an aging arsenal that can be produced without abandoning the nation's unilateral moratorium on nuclear tests, he said.
To that end, he endorsed a comprehensive test ban treaty if adequate verification measures could be negotiated.
Mr. Gates praised efforts to reduce the number of warheads, and predicted that the United States and Russia would at some point conclude another agreement limiting their arsenals.
David E. Sanger contributed reporting.