Americans must prepare for the possibility that a large-scale terrorist attack could take hundreds of thousands of lives, a panel warned a crowd of more than 100 at the ARCO Forum last night.

The panel, titled "Catastrophic Terrorism: The Ultimate Threat," included experts on biological, chemical and nuclear terrorism from the Kennedy School of Government (KSG) and the Faculty of Arts and Sciences.

"We're not talking about the disappearance of a building in Oklahoma City but the disappearance of Oklahoma City," said Ashton B. Carter, Ford Foundation professor of science and international affairs at the KSG.

The panelists said they think large-scale "catastrophic terrorism," as opposed to smaller events like hijackings and pipe bombings, will be increasingly likely in the near future.

A major terrorist attack is "the single largest, most urgent, most imminent threat" facing U.S. national security, said Dillon Professor of Government Graham T. Allison '62, who moderated the panel.

Allison is the director of the KSG's Belfer Center for Science and International Affairs, which co-sponsored the event.

The speakers noted that the danger of an individual dying in an attack is still relatively slight.

"This is an issue of national security policy, not of public safety," said Richard A. Falkenrath, an assistant professor of public policy at the KSG. "You don't need to go home tonight...and buy a gas mask."

Nevertheless, Carter said, the government needs to address the problem now rather than in the panic-stricken atmosphere after the fact.

"[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.

"It's like painting a bulls-eye on your T-shirt and saying, 'Here, aim,'" Meselson said.

During the questioning period, one audience member received scattered applause upon asking whether U.S. attacks on targets in Yugoslavia and Sudan were themselves a form of terrorism.

Carter said the question was an important one.

"One person's terrorist is another person's freedom fighter," he said. "I don't rule out that governments can't behave terroristically."

Attendees said the event helped them appreciate the dangers Americans may face from large-scale terrorism in the future.

"This increased my awareness," said Jeff Roquen of Boston. "I don't think anyone would deny this is a possible threat to the future."