LOS ANGELES - A radiological "dirty bomb" detonated at the Los Angeles and Long Beach ports could cost the nation's economy $34 billion, researchers say.

Experts discussed the potential loss during a conference Saturday examining the economic impact of terrorism.

The symposium, which drew researchers from about a dozen universities and think tanks, was hosted by the University of Southern California's Center for Risk and Economic Analysis of Terrorism Events.

Among the topics were the effects a radiological attack might have on the nation's power grid, the impact on transportation if Seattle bridges were destroyed and efforts to strengthen port security.

Using a mathematical model, researchers from USC and Texas Southern University in Houston predicted the cost of a dirty bomb at the two ports, which together make up the country's largest port complex.

Clark Abt, who manages a social and economic policy research and consulting firm, stressed the importance of funding overseas scanners to detect nuclear weapons before they reach U.S. shores.

"The Coast Guard and Customs are used to drugs," Abt said. "Getting most of it is good enough. But they can't afford to allow a single nuke into New York Harbor."

The university's center received a $12 million grant from the federal Department of Homeland Security in March to find ways to assess outcomes of a possible attacks.