In U.S., Terrorism's Peril Undiminished

For all the work of the national laboratories, there have been no dramatic changes recently in the available instruments. "Until we can change the laws of physics we're not going to make the detectors a great deal better," a knowledgeable official said.

"It's not going to be about the technology," the official said. "It's going to be about intelligence. I am 100 percent sure we will fail if you tell me there's a nuclear weapon 'somewhere in New York City.' If you tell me Lower Manhattan, the odds are a little bit better. If you tell me a neighborhood, we will probably find it."

In the field of biological weapons, there is almost no prospect of detecting a pathogen until it has been used in an attack. After settling a long argument over smallpox inoculation, the Bush administration is working through scenarios in which a large-scale disease outbreak takes place.

"The United States may have to declare martial law someday," Downing said, "in the case of a devastating attack with weapons of mass destruction causing tens of thousands of casualties. This could mean that the military would be given the authority to impose curfews, protect businesses and communities, even make arrests."

Governors normally have jurisdiction over public health emergencies, but a widespread biological attack would cross state boundaries. Secretary of Health and Human Services Tommy G. Thompson has the power to declare a national public health emergency, in which he could impose a quarantine and require inoculation or treatment of unwilling citizens in the name of public health.

But Thompson has no troops at his direct disposal, and the Bush administration is still working through the complex questions of his relationship to the military's new U.S. Northern Command, which is responsible for homeland defense.

Julie L. Gerberding, director of the Centers for Disease Control and Prevention in Atlanta, will have her first extended meeting with Air Force Gen. Ralph G. Eberhart, who heads the Northern Command, in January. She said the two institutions needed "to touch base and identify any gaps in what we understand to be our respective roles."

Some government exercises run to date have used scenarios in which quarantine is breached and a disease spreads uncontained.

"Remember," Gerberding said. "These are imaginary experiments . . . so we decide how we're going to handle it."

Because defending against even the highest-priority threats is so difficult, offense has been at the center of Bush's thinking.

But his favored strategy -- decapitating al Qaeda by hunting down its three dozen top leaders -- has had mixed results elsewhere. Japan's Aum Shinrikyo cult, which unleashed a nerve gas attack in Tokyo's subway system, withered with the arrest of its founding generation of leaders. In the Middle East, the Islamic Resistance Movement, or Hamas, and Palestinian Islamic Jihad have grown new leaders and redoubled their suicide bombing attacks in the face of Israel's relentless campaign of "targeted killings."

"As we go after some of these" al Qaeda leaders, "some of them will get replaced," said the official made available by the White House for answers on strategy. "It doesn't appear they can replace them with people of the same quality and training." He acknowledged, however, that "we don't know these [new] guys in great detail."