"[The potential reaction] leads me to fear the day after an event like this as much as the event itself," he said.

The problem is particularly difficult to address because the dangers come from within the U.S. as well as from foreign countries, one speaker said.

"The biggest terrorist threats to America are Americans," said Elaine Kamarck, a lecturer in public policy at the KSG and a former White House advisor. "They're here, in Columbine High School, in the militias."

Despite their agreement that the government is unprepared to meet the danger, the speakers were unable to settle on specific precautions that should be taken.

Kamarck said public officials and military leaders have been too reticent in discussing the threat.

"The government may not be talking about this, but Hollywood is," she said. "Go to the movies, and the bad guys are some breakaway Soviet republic with some horrible weapon...The popular culture is permeated with this."

But Cabot Professor of the Natural Sciences Matthew S. Meselson disagreed, saying public discussion would give ideas to would-be terrorists.