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.