Officials at the Department of Homeland Security have overstated the performance of costly new radiation detectors designed to prevent the importation of radiological materials that could be used in bombs, according to an unreleased government report.

Brian Michael Jenkins, a longtime terrorism expert with the RAND Corporation, says in this interview that the threat of nuclear terrorism lies more in the realms of Hollywood dramas and terrorist dreams than in reality. He argues that political leaders should not exaggerate the dangers of nuclear terrorism as the fear this creates plays into the terrorist strategy.

The international community must agree on a common set of security standards to ensure that plans to expand the use of nuclear power do not increase opportunities for terrorists or rogue nations to acquire sensitive materials, according to Thomas D’Agostino, head of the National Nuclear Security Administration.

Top federal officials and medical experts gathered in Washington on Thursday to consider this nightmare vision. Their conclusion: Cities and states are frightfully ill-prepared for dealing with an attack using a small nuclear bomb.

An evolving U.S. national policy aims to create a system of nuclear forensics, in which scientific analysis could quickly identify the source of a nuclear attack or attempted attack.

A nuclear device assembled by terrorists is likely to have a "relatively low yield," much smaller than the 10-kiloton weapon dropped on Hiroshima at the end of World War II, according to the chief nuclear scientist with the U.S. Homeland Security Department. Nevertheless, even a small nuclear explosion would probably be viewed as a "success" by any nonstate actor.

With construction of many new nuclear reactors under discussion, the Nuclear Regulatory Commission is grappling with the question of whether they should be designed to withstand a Sept. 11 style airplane attack.

Adequate planning for the aftermath of an act of nuclear terrorism could save hundreds of thousands of lives, but nearly five years after the attacks of Sept. 11 those contingency plans still do not exist, according to a report released last week by the Physicians for Social Responsibility.

The interagency network responsible for defending the United States against nuclear terrorism is compiling a global database of nuclear "fingerprints" in an effort to trace fissile material to a source in the event of a nuclear attack.

President Bush and President Vladimir V. Putin of Russia announced a new global program to track potential nuclear terrorists, detect and lock up bomb-making materials and coordinate their responses if terrorists obtain a weapon, according to administration officials who have negotiated the deal.