Clad in jet black from helmet to boots, Singapore coast guard commandos dashed up the gangplank. Responding to a simulated report of a terrorist bomb planted on the hulking cargo ship, they proceeded in a half-crouch along the starboard deck, peering through the sights of German-made assault rifles.

As sirens on the adjacent wharf wailed, dozens of other uniformed Singaporeans joined the practice on-ship hunt: blue-bereted special operations police, soldiers in green camouflage with a sniffer cocker spaniel and the bomb disposal squad from the navy's diving unit.

This was Singapore's first effort at a joint response by its security forces to a potential terrorist attack off the world's second-busiest port. But the exercise, staged one morning last month, also pointed up the limited ability of countries in the region to cooperate in countering the maritime threat.

Despite the urging of security experts that the island city-state and its neighbors work together more closely against terror threats in the waters of Southeast Asia, this was exclusively a Singaporean affair. Officials from the United Nations, the U.S. Coast Guard and China's maritime security agency attended, but only as observers.

Much of the concern focuses on the Strait of Malacca, a vital marine artery for more than one-quarter of the world's trade and half its oil, including most of the fuel bound for Japan, China and South Korea.

Adm. Thomas B. Fargo, commander of U.S. Pacific Command, proposed an initiative this spring to enhance intelligence-sharing with Asian governments and to coordinate the interdiction of terrorists at sea. "This collective effort will empower each participating nation with the timely information and capabilities it needs to act against maritime threats in its own territorial seas," Fargo said in a speech last month.

But the response has been uneven. Efforts to build a regional approach are hampered by national rivalries, equipment shortages and an acute sensitivity, particularly by Malaysia and Indonesia, about maintaining control of their territorial waters.

When Fargo told a U.S. House committee in March that he was considering putting U.S. Marines aboard high-speed vessels to capture terrorists in the Malacca Strait, officials from Malaysia and Indonesia, whose countries border the waterway, balked. Malaysian Foreign Minister Syed Hamid Albar said terrorist threats were exaggerated and warned against unilateral U.S. action in Malaysian waters.

U.S. diplomats have continued to lobby for a more muscular approach, while trying to reassure Southeast Asian leaders that Fargo's initiative is not a ruse to deploy U.S. forces in the sea lanes. U.S. Assistant Secretary of State James A. Kelly pressed the issue at a regional security forum in Indonesia last month, while Gen. Michael Hagee, commandant of the U.S. Marine Corps, made his first trip to Singapore a week earlier for similar discussions.

Singapore, a close U.S. ally with a modern economy that is dependent on international trade, got on board early. Previously targeted by a militant underground group linked to al Qaeda, Singapore is one of the first maritime nations to comply with new U.N. rules to protect ports against terrorism, which include periodic exercises.

At 9:03 the morning of last month's drill, an alert sounded on the APL Japan, a Singaporean cargo ship with metal containers stacked four high on deck.

"Secure all areas! Stop cargo operations! Go now!" barked Chief Officer Cheong Kwee Thiam, gesturing to the crew. The men, in white jumpsuits, fanned out along the vessel, as long as three football fields.

At 9:30 a.m., Cheong's two-way radio carried a new alert. A bomb was hidden somewhere on board. As sirens screamed, the commandos streamed aboard. The police found the mock explosive in a cardboard juice carton in a bin in a cargo bay. The bomb squad was summoned, and an explosive ordnance disposal specialist squeezed the trigger on a device that shot a high-powered jet of water into the simulated bomb to disable it.

About 20 minutes later, the action shifted to portside as a small boat suddenly appeared from behind a neighboring wharf and raced toward the APL Japan. In the exercise, it was a possible suicide bomber intent on ramming the vessel.

Two port authority patrol boats darted in from two directions to head off the intruder. A Coast Guard patrol boat sped to the scene moments later, followed by a navy vessel.

This simulated strike was loosely modeled on an attack in October 2000, when al Qaeda operatives in Aden, Yemen, plowed a dinghy laden with explosives into the USS Cole, killing 17 U.S. sailors.

Although Singapore has not had a similar bombing, radicals linked to al Qaeda have planned several attacks around the island nation, according to U.S. and Singaporean officials.

In 2001, Singaporean investigators discovered that the regional terror organization Jemaah Islamiah was studying the viability of a seaborne suicide attack against U.S. naval vessels in the Johore Strait off Singapore's northern coast.

Authorities searching a Jemaah Islamiah operative's house found a map of the island with "significant markings," according to Minister for Home Affairs Wong Kan Seng. These included a kill zone where the channel is narrowest, leaving a ship no room to avoid colliding with a suicide vessel. The plan also provided for taking advantage of inlets to hide the attack vessel from radar, Wong said in an e-mail reply to questions.

Further suspicions about terrorist plots were raised when U.S. intelligence agents in Afghanistan recovered surveillance tapes from an al Qaeda safe house that showed Malaysian navy ships on patrol in the Malacca Strait. Jemaah Islamiah has also filmed wharves, the Changi Naval Base and warships in the area, Wong said.

Wong stressed that the high incidence of piracy attacks in the region compounds the problem. "If such acts of piracy can occur, so too can acts of shipjack or terrorism," he said. "Operationally, the line between these acts is thin."

The private International Maritime Bureau reported that of 445 piracy attacks recorded worldwide last year, more than one-quarter were in Indonesian waters. Indonesia also logged the highest number of attacks, 21, during the first three months of this year.

Wong warned of the possibility that a fuel tanker might be hijacked and turned into a floating bomb to attack ports or other ships.

An attack that blocked the Malacca Strait, a 500-mile channel running between the Indonesian island of Sumatra and the Malaysian peninsula to Singapore, would badly hurt world trade, forcing vessels to make long detours and substantially boosting shipping costs.

Before Fargo began promoting his regional approach, the U.S. government launched a worldwide security initiative for shipping containers, which calls for U.S. Customs officers to work with local inspectors to screen out nuclear, chemical and biological weapons in cargo bound for American ports. The United States also has begun a proliferation security initiative to intercept weapons of mass destruction smuggled by land, sea or air.

By July, ships and commercial ports must meet new maritime security rules set by the U.N. International Maritime Organization. Less than 6 percent of ports worldwide and 10 percent of ships now comply with the rules, according to IMO Secretary General Efthimios Mitropoulos. Singapore was among the first to meet the requirements.

The new rules also require all 46,000 ships involved in international trade to have a security alert system that could send a distress signal to the nearest on-shore location without alerting hijackers. But Michael Richardson, visiting senior research fellow at the Institute of Southeast Asian Studies here, said that savvy terrorists might know where the buttons are located and take preventive action.

After the Sept. 11, 2001, attacks in the United States, Singapore adopted several measures to improve port security. They require that oil tankers and other vessels at risk give 24-hour notice of their arrival and follow designated routes. Their movements are tracked by high-tech identification systems. Sensitive locations, such as petrochemical facilities, are now off-limits to most vessels.

But other Southeast Asian countries, notably Indonesia, lack the resources to adopt such safeguards. Indonesia has only 117 naval vessels, from patrol boats to warships, to protect the waters off its 17,500 islands, said Chief Adm. Bernard Kent Sondakh. And only 30 percent of the vessels are seaworthy, he said.

Singaporean commandos search for a bomb aboard a ship during an anti-terror exercise in Singapore Harbor.