A U.S. law that will require foreign ports to scan every container they ship stateside looks set to create big winners and losers and force consolidation at ports around the world.

Designed to ensure freight containers aren't used by terrorists to smuggle weapons or bomb materials into the U.S., the Law on Maritime Cargo Scanning Requirements is shaping up to have a dramatic impact on the global shipping industry, port officials and operators in Europe and Asia say.

Companies that make the giant $5 million X-ray or gamma-ray machines needed to scan shipping containers are anticipating a boom in orders as roughly 700 ports around the world gear up for the U.S. rules, which were signed into law in August but take effect in 2012. Industry analysts say each will have to buy one to 10 of the scanners or stop exporting to the world's richest market.

Large modern ports, mostly in Asia, also expect to win new business as smaller and older ports struggle to meet the U.S. requirements. The European Union estimates the average start-up cost for a port to buy and support the scanners will be around $100 million, too much to make business sense for some minor ports to go on shipping to the U.S.

Big, older river ports like Antwerp in Belgium are also at a disadvantage. Antwerp would need to build new roads and bridges to get all containers to scanners from its scattered docks and may not be ready in time. ''We're looking at billions [of euros] in extra spending,'' says Lieven Muylaert, a Belgian customs official.

The EU has led opposition from around the world to the new U.S. requirements, worrying the relative lack of flexibility at many European ports will add to cost advantages Asian exporters already hold over European companies. Asia's newer ports tend to be bigger, but more compact, than their European counterparts. They will have less trouble meeting the requirements, port operators and analysts say. The EU has threatened to impose reciprocal constraints on all containers landing in the EU from the U.S.

Since the attacks of Sept. 11, 2001, the U.S. has toughened rules that aim to stop terrorists from smuggling weapons into the country in containers, the 20- or 40-foot steel boxes that carry everything from bananas to toys to lawn mowers around the globe. The U.S. imported 12 million containers of goods last year, and that number is expected to rise, according to the U.S.

Security experts say the container-scanning law may reduce, but won't eliminate, the risk of terrorists smuggling weapons aboard ships. That is partly due to the poor resolution of X-rays able to scan something as big as a container, according to Jim Cowling, managing director for Maritime Security Solutions Ltd., a London-based consultancy. It is also because ships remain vulnerable to tampering after leaving port. ''It could be possible to hijack or bribe a ship and put a container on it in the middle of the ocean,'' says Mr. Cowling.

The new U.S. scheme will replace the current risk-based system, under which only selected containers get scanned. Under the new system, giant X-ray devices would scan every container for suspicious shapes at a rate of about three containers per minute. It now takes several minutes to scan a container.

The three main international suppliers of container scanners are Nuctech Co., a Chinese state-owned company that dominates in Asia; U.S. defense contractor Science Applications International Corp., which sells mainly in the U.S.; and Smiths Heinmann GmbH, part of Smiths Group PLC, a pan-European firm. All three compete in Europe and Latin America. A fourth company, Rapiscan Systems, a division of OSI Systems Inc., also makes scanners but is behind the others in orders, say analysts.

Michel Lequy, who sells Nuctech scanners in Europe, says orders already grew to dozens per year from low single digits before U.S. lawmakers started talking about the scanning law in 2003. He expects a further increase after governments and ports start budgeting for the actual law next year. ''We can cash in on a boom,'' he said.

Though Europe's governments are likely to pick up much of the extra cost for major ports like Antwerp to meet the rules, construction can take years in the face of tough EU environmental laws, putting them at a significant disadvantage.

Antwerp's troubles, could mean more business for the nearby Dutch port of Rotterdam, which is more compact than Antwerp and expects to be able to install the scanning equipment quickly and at comparatively low cost. ''Security is a good business opportunity,'' says Peter Struijs, chief operating officer at Rotterdam.

Without significant change to the rules, smaller ports such as Seville in Spain, Dunkirk in France and Naples, Italy, could have to stop shipping to the U.S. altogether. ''The law will force us to stop shipping to the U.S., unless we can attract a lot more customers, which would justify investment in the equipment,'' says Philippe Revel, manager for the shipping terminal at Dunkirk.

The Bush administration has said it wants to cut the number of ports that ship containers to the U.S. to around 100 world-wide, from 700 today because that would make it easier to monitor security. Consolidation would also force more trucks onto Europe's already congested roads, however, as they move U.S.-bound goods to bigger, but more distant, ports for shipping.

Port operators say the biggest long-term cost of the U.S. rules may be the extra ''dwell time'' -- the number of days that containers packed with goods spend sitting on docks, clogging terminals and delaying shipments, before they head out to sea. Operators estimate average dwell time will increase to seven days from around five after 2012.

Port officials say the impact of the new law could be softened if the U.S. agrees to let companies such as Wal-Mart Stores Inc., which fill their own containers, to scan containers themselves. Wal-Mart campaigned against the law.

''We shouldn't have to put those containers through an X-ray machine,'' says Andreas Mai, harbor master at Bremerhaven, a German port that ships over a thousand containers a day to the U.S., carrying everything from Mercedes car parts to Red Bull soft drinks.

Mr. Mai has been lobbying U.S. officials to implement the new law so that ports would have to scan only containers packed by individuals or small businesses. One U.S. Customs official said Washington would listen to such concerns. ''We know this is a work in progress,'' the official said.