In a speech in Brussels, Napolitano said security and customs authorities needed to work closer with industry to develop new technologies and share information to track chemicals that can be used to produce weapons.
Not enough effort is made, she also said, to minimise potential disruptions to trade and transport in case major infrastructure hubs are damaged by attacks.
"Consider the consequences of such an attack ... Beyond the immediate impact ... the consequences could quickly snowball and impact economies around the world," Napolitano said during a two-day visit to meet European Union officials.
"People across the world would find empty store shelves and serious shortages in needed medical supplies," she said.
Governments across the world have been reviewing aviation and transport security since U.S.-bound parcel bombs sent by air from Yemen were intercepted in Dubai and Britain last October.
In the EU, the bloc's 27 governments are preparing a plan on how to screen cargo from third countries, although a German proposal for a "blacklist" of airports with insufficient security standards for cargo has been rejected.
But calls from more screening of shipments have led to clashes with industry in the United States and Europe as transport companies grew concerned over the cost of tighter security, particularly of sophisticated imaging technology designed to detect explosives.
Addressing such concerns, Napolitano said while new technologies would be used, intelligence-gathering and new standards were also an important tool. The United States would also send "hundreds" of aviation and customs officials to help protect transport hubs.
She said joint efforts by customs authorities from the United States and other countries have helped investigate smuggling of chemicals that could be used to make explosives into Afghanistan and Pakistan in the last year.
In the United States, she said, authorities wanted to work with industry on developing tracking mechanisms for export goods.
"We will work with institutions ... ranging from hospitals and laboratories all the way to beauty supply companies to prevent the diversion of dangerous chemicals for use by terrorists," Napolitano said.
U.S. security authorities would also seek help from the World Customs Organisation and international transport bodies to plan for major transport disruptions after an attack, Napolitano said, without giving details.
"Global trade cannot grind to a halt as governments and industry figure out what to do," she said. (Reuters)
