WASHINGTON/LONDON (Reuters) - The United States denied entry to a Bolivian-flagged freighter on Thursday as tough new global laws to protect shipping from terrorist attacks took effect with little disruption to global trade.

Washington, fearing an attack or infiltration by al Qaeda from the sea, has vowed to police the new United Nations codes strictly by turning away ships that are not security-certified or delaying ones that have called at "contaminated ports."

The U.S. Coast Guard said it ordered Bolivian-flagged cargo ship Dahomey Express to leave U.S. waters because it lacked the new security certificates. The United States was a major driving force behind the law, and is being seen as a litmus test for the new codes' effectiveness.

Coast Guard spokeswoman Jolie Shifflet said the vast majority of the roughly 250 ships arriving in the United States on Thursday received the green light for entry.

On the eve of the July 1 deadline to implement the new anti-terrorism measures, only about half of the world's ports and 53 percent of global shipping had complied with the International Ship and Port Facility Security code, or ISPS, according to the U.N.'s International Maritime Organization, its chief architect.

Shipping sources warned that despite the relatively smooth first day, it was too early to say the transition to the new regime had been a success, adding it would take days and weeks to get a full picture of compliance.

Rupert Herbert-Burns, a senior consultant with the Maritime Intelligence Group which advises ports on security threats, said the ISPS was a good step, but no panacea to wipe out security threats.

"There are still thousands of port facilities around the world, particularly in the less developed world, which won't be in compliance for some time. That is obviously of concern," he said. "It's not going to be watertight until you've got much, much more endemic coverage."

Nigeria, for example, had said on Thursday that just three of its 53 port terminals were ready. But it showed little immediate concern over flunking the deadline and said the compliance problems would not affect its precious oil exports.

SMOOTH SAILING IN ASIA, EUROPE
The ISPS code, signed by 147 governments, requires ports, stevedoring companies and owners of ships larger than 500 tons to draw up plans for responding to a terror threat, implement tighter security around facilities and train staff.

In Asia, where most major shipping lines and key container ports had met the U.N.'s July 1 deadline, there were no initial reports of delays.

At the world's largest transshipment hub in Singapore, all 41 ships that visited the port by 0200 GMT on Thursday were compliant.

Traffic at Taiwan's two main international ports of Kaohsiung -- the world's sixth-largest container terminal -- and Keelung moved swiftly throughout the day, with no vessels requiring searches, harbor officials said.

Australia, where all ships and ports involved in international trade met the ISPS deadline, was keeping a wary eye on suspect vessels but did not delay any.

In Europe, where most mega-ports were in full compliance, there were also no reports of early snags.

A spokesman in Rotterdam, Europe's biggest port, said he did not foresee any disruption to trade or major incidents involving non-compliant ships.

"We are at the center of the big cargo shipping lanes, so ports like ours, have been very security conscious for years. Shady shipping lines and murky flags of convenience are unlikely to call here as we are at the top of the pyramid," the spokesman said.

He said even if a ship were to arrive without a ship security certificate it would not be turned away or even fined because the Netherlands had "no legal basis" to do that.

Germany's Transport Ministry said uncertified vessels were still being allowed to dock, although ships from a high-risk region that had made no attempt to comply might be stopped from doing so.

The Paris MOU, which overseas maritime safety and security in 13 EU countries, as well as Russia and Canada, reported it was business as usual.

By Caroline Drees and Stefano Ambrogi