The Bush administration is developing a new strategic doctrine that moves away from the Cold War pillars of containment and deterrence toward a policy that supports preemptive attacks against terrorists and hostile states with chemical, biological or nuclear weapons.

The new doctrine will be laid out by President Bush's National Security Council as part of the administration's first "National Security Strategy" being drafted for release by early this fall, senior officials said.

One senior official said the document, without abandoning containment and deterrence, will for the first time add "preemption" and "defensive intervention" as formal options for striking at hostile nations or groups that appear determined to use weapons of mass destruction against the United States.

Bush hinted at the new doctrine in his State of the Union address in January, when he labeled Iraq, Iran and North Korea an "axis of evil" and warned that he would not allow them to threaten the United States with weapons of mass destruction. The president articulated the doctrine for the first time June 1 in a commencement address at West Point.

By adopting the doctrine as part of its formal national security strategy, the administration will compel the U.S. military and intelligence community to implement some of the biggest changes in their histories, officials said. That is already touching off heated debates within the administration and among defense commentators about what changes need to be made and whether a doctrine of preemption is realistic.

But there is general agreement that adopting a preemption doctrine would be a radical shift from the half-century-old policies of deterrence and containment that were built around the notion that an adversary would not attack the United States because it would provoke a certain, overwhelming retaliatory strike.

Administration officials formulating the new doctrine said the United States has been forced to move beyond deterrence since Sept. 11 because of the threat posed by terrorist groups and hostile states supporting them. "The nature of the enemy has changed, the nature of the threat has changed, and so the response has to change," said a senior official, noting that terrorists "have no territory to defend. . . . It's not clear how one would deter an attack like we experienced."

The administration's embrace of the new doctrine has triggered an intense debate inside the Pentagon and among military strategists about the feasibility and wisdom of preemptive strikes against shadowy terrorist networks or weapons storage facilities.

It has aroused concern within NATO as well. Defense Secretary Donald H. Rumsfeld told the United States' 18 NATO allies in Brussels last Thursday that the alliance could no longer wait for "absolute proof" before acting against terrorist groups or threatening countries with chemical, biological or nuclear weapons.

NATO Secretary General George Robertson, reacting to Rumsfeld's remarks, said NATO remained a defensive alliance. He added, "We do not go out looking for problems to solve."

Some defense analysts said preemption carries the risk of causing a crisis to escalate quickly by increasing pressure on both sides to act sooner rather than later -- forcing them, in the parlance of the nuclear chess game, to "use it or lose it."

"Preemption is attractive on the surface," said defense analyst Harlan Ullman. But he added: "As one gets deeper, it gets more and more complicated and dangerous."

Critics also note that a botched attack that blew chemicals, biological spores or radioactive material into the atmosphere would risk killing thousands of people, not only in the target nation, but in neighboring countries.

Even proponents of preemption inside and outside the government concede that this more aggressive strategic doctrine requires far better and far different intelligence than the U.S. government gathers -- at a time when the abilities of the CIA and the FBI to fulfill their current duties are under scrutiny.

Michele Flournoy, a former Pentagon proliferation expert now at the Center for Strategic and International Studies, said that to be effective, the United States will need to strike preemptively before a crisis erupts to destroy an adversary's weapons stockpile. Otherwise, she said, the adversary could erect defenses to protect those weapons, or simply disperse them.

But Flournoy said she favors moving toward a doctrine of preemption given the proliferation of chemical, biological and nuclear weapons among states supporting terrorists. She said the policy may offer the best of a series of bad choices.

"In some cases, preemptive strikes against an adversary's [weapons of mass destruction] capabilities may be the best or only option we have to avert a catastrophic attack against the United States," she said.

Under the doctrine, nuclear first strikes would be considered weapons of last resort, especially against biological weapons that can be best destroyed by sustained exposure to the high heat of a nuclear blast, Pentagon officials said. But the focus of the effort is finding new ways of using conventional weapons to detect and destroy weapons arsenals, and especially the missiles used to deliver them.

To do that, the Pentagon is studying how to launch "no warning" raids that go far beyond quick airstrikes. The key tool to execute that mission is a new "Joint Stealth Task Force" that pulls in the least detectable elements of every part of the armed forces, including radar-evading aircraft, Special Operations troops and ballistic submarines being converted to carry those troops and to launch cruise missiles.

Beyond changes in weapons, doctrine and organization, Rumsfeld and his top aides are trying to alter the U.S. military mind-set. "Preemption . . . runs completely against U.S. political and strategic culture," defense expert Frank Hoffman said in an essay published this year by the Center for Defense Information.

In the past, the United States has viewed surprise or "sneak" attacks as dishonorable, the kind of thing inflicted on the American people, not initiated by them, analysts have noted.

One senior defense official responded that 21st century security threats can no longer be assessed in terms of the past. "In the world in which we live, it's not enough to deter," the official said. "You need more capability, more flexibility, more nuanced options and choices."

Defense scientists and war planners are hard at work developing new weapons and capabilities to give Bush "options different than those he may have had in the past," the official said.

At the Defense Threat Reduction Agency, a $1.1 billion defense agency created in 1998 to counter the threat of weapons of mass destruction, scientists are studying how to attack and destroy hardened and deeply buried bunkers containing chemical, biological and radiological weapons with advanced conventional bombs, low-yield nuclear devices and even high-yield nuclear weapons.

"There was a time during which we really didn't know what phase we were in, so we called it the 'post-Cold War phase,' " said Stephen M. Younger, the agency's director. "And it wasn't clear what kind of weapons we were going to need for the conflicts of the future. September 11 clarified that. And we are getting a better understanding of the types [of threat] we may face in the future and the types of weaponry that will be required [to counter] them."

Younger said his agency is working on advanced conventional explosives with hardened warheads that could penetrate underground concrete bunkers and destroy biological agents with a sustained level of extremely high heat.

"We want to use the minimum force to achieve the military objective, if at all possible, with a conventional weapon," Younger said. "We do not want to cross the nuclear threshold unless it is an example of extreme national emergency."

But there are some bunkers that are "so incredibly hard," Younger said, "that they do require high-yield nuclear weapons." Low-yield nuclear warheads could be useful in certain scenarios, he said, but they run the risk of spreading biological agents across the countryside.

Rumsfeld's Nuclear Posture Review, completed at the end of last year, stated that "new capabilities must be developed to defeat emerging threats such as hard and deeply buried targets." It also said "several nuclear weapons options" that could be useful in attacking such facilities include "improved earth penetrating weapons."

But senior administration officials said the tactical use of nuclear weapons is being studied, not actively contemplated. "There is no one anxious to think about the employment of tactical nuclear weapons," a senior defense official said. "That's not what we are trying to do."

What the Pentagon is most focused on, the official said, is a method of "advanced conventional strike."

Inside the Pentagon, some officials suspect that the new doctrine may be acted upon sooner rather than later.

"I think the president is trying to get the American people ready for some kind of preemptive move" against Iraq, said a Pentagon consultant. He said it would not necessarily be against Iraqi weapons sites but might instead involve a seizure of Iraqi oil fields.

But a senior administration official dismissed the idea of a "bolt from the blue" attack on Iraq. "I want to caution that [the president] was not making an announcement about imminent action" in his West Point address, the official said. "Some people have quite frankly said, 'Oh, this must have been about Iraq.' He was not making an announcement about imminent action, but this was a doctrinal statement."

Rumsfeld may have captured this situation best when he declined to discuss preemption last week. Asked in an interview whether the U.S. government is contemplating preemptive moves against other nations' weapons of mass destruction, he replied: "Why would anyone answer that question if they were contemplating it?"

At West Point, President Bush said U.S. strategy must go beyond deterrence to deal with terrorists, who have no territory to defend.