Modern-day buccaneers no longer hoist the Jolly Roger and swing on to Spanish galleons brandishing cutlasses.

They are more likely to arrive in the dead of night, clambering up onto oil tankers with grappling hooks flung from their inflatable dinghies. They wear military camouflage and hoods and tote machine guns and grenade launch-ers.The last existing stronghold of piracy, in the South China Sea and the Straits of Malacca off Malaysia, was broken after the Opium Wars in the late 19th century.

But seafarers in Southeast Asian waters have remained under attack. In the late 1970s, Thai pirates began preying on Vietnamese boat people fleeing southern Vietnam, robbing, raping and occasionally killing their victims.

Today, pirates in the region are especially brazen.

"We didn't have professional pirates like these 10 years ago," said P. Mukundan, director of the London-based International Maritime Bureau, which runs the Regional Piracy Center in Kuala Lumpur.

"Today, we are seeing quite a number of these attacks. There's also been an increase in the violence and audacity in their attacks."

Just last month, the Malaysian-registered tanker Petro Ranger set sail from Singapore for Vietnam laden with diesel and kerosene. On the evening of April 17, pirates took over the ship and it turned up about one week later in China.

Since 1991, when the piracy center began gathering data, the number of reported attacks each year worldwide has more than doubled from 107 to 229 in 1997. More than half occurred in Asia, whose waters are flecked with small islands.

Ships are especially vulnerable when they gingerly navigate the narrow channels between the islands, which are ideal hideouts for pirates with swift motorboats.

The seas off Indonesia, Thailand and the Philippines are the most dangerous.

No longer content with filching radio equipment and nets from fishermen, the modern swashbucklers are targeting tankers and bulk carriers. Heavily armed, they take ships' crews as hostages and demand ransom, and sometimes they steal the whole ship.

Last year, pirates killed 51 seamen, compared to 26 in 1996.

The International Maritime Bureau warned in its March bulletin that the Asian economic crisis threatens to worsen piracy around Indonesia, where unemployment and inflation are soaring along with social unrest. With about 13,000 islands extending 3,000 miles along the equator, the Indonesian archipelago straddles essential sea lanes used by ships for trade between Asia and Europe.

"Given that already there has been some social breakdown within the country, it would be all too easy to kick-start the piratical attacks," the bulletin said.

Many ship captains agree.

"There's not much to plunder on land, now that all our economies are down," said Capt. Segar Rajoo, a Malaysian who has sailed dozens of merchant ships on the South China Sea the past 15 years.

"But ships always carry cargo, and every big ship out there is worth millions, even billions," Rajoo added. "And like Captain Hook, ambitious pirates these days want the whole ship."

Within the last six months, three tankers have been hijacked after sailing north toward the South China Sea from Singapore.

There were also dozens of attacks last year in which pirates shackled crewmen, stole their valuables and looted ships' safes.