A new study says security measures should focus on economic recovery after a possible terrorist attack on a U.S. port. The report by the Public Policy Institute of California says attacks cannot be prevented, but preparations can minimize their financial impact, and discourage would-be attackers.

The study by a team of economists and maritime security experts notes that the nation's 361 seaports together handle 40 percent of U.S. international trade. The report says an attack on a major port could cause serious disruptions through the US economy.

"There is an over-emphasis on prevention of an attack at a port, and perhaps not enough emphasis on what happens in response to an attack on the port," said Jon Haveman, a contributing author and co-editor of the report. He says a key theme emerges in the study of port security.

The report says recovery plans should focus on reducing economic panic and restoring supply chains. Haveman says the government needs better ways to prioritize shipments to get essential goods moving .

Essential shipments might include car parts heading for San Francisco, where a major auto plant - a joint venture between General Motors and Toyota - produces hundreds of thousands of vehicles a year.

The report says if terrorists were to blow up highway and rail bridges at the joint ports of Los Angeles and Long Beach, the attack could eliminate half of the ports' capacity and lead to an economic loss of $45 billion. Haveman calls that a serious toll, but says it is one that the U.S. economy can handle.

He says advance planning is difficult. At the Los Angeles-Long Beach port, it involves coordinating 15 separate government agencies. But he says advance planning is essential.

"That makes fundamental sense in its own right, and it also makes sense as a deterrent, because if we can eliminate the economic consequences of an attack or substantially reduce them, then we're less likely to have the attack in the first place," he said.

He says the goal of terrorists is to disrupt the economy, and that preparations to limit the impact of an attack will decrease the risk of having one.