Asa Hutchinson, undersecretary for border and transportation security, told a Senate hearing that "most experts believe that a terrorist attack using a container as a weapon is likely." U.S. officials have "no specific information that there is more increased jeopardy than a month ago," he said, and no specific port or region has a higher risk of attack.

"Because of the sheer volume of sea container traffic and the opportunities it presents for terrorists, shipping is uniquely vulnerable," said Hutchinson, who works in the Department of Homeland Security. He cited as an example of the threat the discovery in Italy of a man traveling in a Canada-bound shipping container with false security documents after the Sept. 11 attacks.

The U.S. now inspects 4 percent of the 6 million shipments that arrive at more than 100 ports, twice the 2 percent before the Sept. 11 attacks in 2001. About 20 percent of that cargo passes through overseas ports such as Hong Kong, where U.S. inspectors are being stationed. Cargo worth $1.2 trillion, or half of U.S. imports, arrives by sea. The rest comes from Canada and Mexico.

"What we are looking for is anomalies," such as the origin, type of cargo and the integrity and identification of the company shipping the goods, Hutchinson said. Among the threats are efforts by terrorists to recruit smugglers who know how to get people, drugs and weapons into the U.S., he said.

The U.S. has tried to step up security by requiring all cargo lists to be submitted for Customs review before a container is loaded. The U.S. also has signed agreements with more than 2,000 companies to increase cargo inspections and testing of satellite tracking to block tampering of shipments en route.

The U.S. opened the war last night by firing as many as 40 cruise missiles in an effort to take out the Iraqi leadership, officials said.