U.S. and regional security officials are especially concerned about the vital Malacca Strait, the narrow waterway linking Asia to the Middle East and Europe. This sea-lane running past Singapore, Malaysia, and Indonesia is one of the busiest and most important in the world. More than a quarter of the world's trade and about half its oil passes through the strait each year.

The strait also is infested with pirates, particularly in Indonesian territory.

Security experts paint vivid pictures of how terrorists could take advantage of lax security to blow up tankers, or take over ships to use them as floating bombs or launching pads for nuclear attacks.

Jeffrey Chen, a maritime security expert at Singapore's Institute of Defense and Strategic Studies, says these scenarios are not far-fetched.

"Within Southeast Asia, there is a strong anti-American, anti-Western sentiment and these then make the chances of maritime terrorism attacks very likely," he said. "I do not think it is that easy. It would take a lot planning, a lot of expertise, a lot of luck."

But Michael Richardson, a researcher at Singapore's Institute of Southeast Asian Studies and author of a report on maritime security, says it would not be difficult for terrorists to hijack ships. He says that is in part because it is possible to buy false qualification certificates for seafarers.

"It would be relatively easy for terrorists to use the existing seafarer recruitment and manning scheme, which is riddled with abuse and corruption, to put sleeper crews on ships and commandeer them at the right time and take control of the ship," Mr. Richardson said.

Hartmut Hesse is the deputy director of the United Nations' International Maritime Organization, or IMO. He says all transport is vulnerable since the terrorist attacks in the United States on September 11, and says last month's rail attacks in Madrid prove the point.

"International security measures were long overdue in the shipping industry," he said. "After 9/11, there was an urgent need to put security measures in place. We have now seen Madrid, which was a different mode of transport, rail in this case. This seems to be conveying the message that transport seems to be an easy target."

Given these concerns, the maritime industry and member nations of the IMO, are implementing stricter security rules for ports and shippers. The new code, called the International Ship and Port Facility Security Code requires security certification for ships and ports, and crewmember screening.

The requirements start July 1. Important port cities in Asia, such as Hong Kong and Singapore, say they will make the deadline. On top of that, Hong Kong, Singapore and Malaysia are already cooperating with a new U.S. customs rule called the U.S. Container Security Initiative.

The initiative uses intelligence gathered by customs officials around the globe to identify suspicious containers, which are then X-rayed and if necessary, unloaded and examined by hand.

The U.N. International Labor Organization also is introducing seafarer identification cards using finger or retina prints, making them harder to forge. Because the new technology is expensive, many developing nations are having trouble complying with the new security codes. Industry experts say the Philippines and Indonesia face an especially daunting task, with their many islands and dozens of ports. Both countries also are poor.