ABOARD THE USS SAMPSON IN THE RED SEA -- Lt. Eric Alfaro's heart races each time he straps a pistol on his hip, grips the rope handle of a swaying pilot's ladder and clambers up the steep hull of a foreign merchant ship that has been challenged by his captain.

"You just have no idea what to expect when you reach the top of that ladder," said the Navy boarding team officer from Annandale, Va. "I'm always a little bit afraid when I go on board."

Alfaro and his armed 12-man squad are among the front-line enforcers of the U.N. trade embargo against Iraq. In the past four months, gun-toting sweep teams have crossed the choppy seas in battered whale boats and Navy SEAL commando units have dropped out of helicopters to search merchant ships -- 713 -- plying the Red Sea, Persian Gulf and northern Arabian Sea.

In their hunt for Iraqi contraband, they have encountered hostile merchants, a boatload of sheep, a drunken South Korean crew mourning the death of the ship's cook and more huge rats than they care to recount.

Armed with hammers, crowbars and metal cutters, they have pried open thousands of containers of car parts, military hardware and household goods. They have inspected tons of foul-smelling fertilizers and investigated hundreds of containers of chemicals.

Most Iraqi merchant ships took refuge in Middle East harbors in the early days of the interdiction efforts and have stayed there. As a result, U.S. and other naval vessels have had to bar only 30 vessels attempting to enter or leave ports in the region. Most of the diversions have resulted from incomplete cargo information or contradictory destination details. Only six of the vessels contained shipments bound for Iraq, according to Navy authorities.

While reports of the trade-busting ship boardings have become almost routine addenda to Pentagon news briefings, tension remains high among the squads charged with carrying out the international orders.

"If somebody were really intent on setting a trap, it would be a death trap," said Capt. Joseph S. Mobley, who commands the USS Saratoga, mother ship of the carrier battle group assigned to policing the northern Red Sea. (Twenty-one Saratoga crew members drowned last week when a ferry capsized while transporting them from shore leave in Haifa, Israel.)

More than 90 percent of all the ship boardings in the interdiction effort have occurred in the northern Red Sea, where a multinational force of ships has established a "gate guard" at the entrance to the Gulf of Aqaba, passageway to the Jordanian port of Aqaba, the primary docking point for Iraq's sea trade.

The U.S. warships, as well as combat vessels from a half-dozen other nations, are assigned operating areas with nicknames such as Toto, Oz, Wizard and Emerald City, the creation of an admiral responding to one staff aide's observation that "I don't think we're in Kansas anymore."

All merchant ships steaming past the peaks that jut from the Sinai Peninsula at the mouth of the Gulf of Aqaba are questioned by warships on patrol. Since the sanctions were imposed in mid-August, about 5,830 ships in the Red Sea and Persian Gulf have been ordered to identify themselves and describe their cargoes and destinations.

Most respond to the queries and offer little resistance. A few vessels, particularly those operated by Iraqi crews, have refused to stop even after gate guard ships fire warning shots. U.S. officials said some Iraqi merchant masters have told them Iraqi President Saddam Hussein has threatened to execute any merchant commander who stops his vessel in compliance with the U.N. mandates.

But rather than firing disabling shots at ships that refuse to stop, the Navy dispatches its SEAL (Sea-Air-Land) commando teams to board the vessels. The heavily armed teams slide down ropes onto the decks of moving ships and conduct their searches.

"The SEALs are the 'Make my day' kind of guys," said Ensign Thomas Owens, who heads the Coast Guard law enforcement unit assigned to the Sampson boarding team. "That gets their attention."

Cmdr. William D. Sullivan, a resident of Woodbridge, Va., until he took command of the Sampson late last summer, said most of the ships that refuse to stop "are found to be innocent; they're just being stubborn."

Once the teams board the vessels, Owens said, "a lot of crews are offended by weapons being drawn on them. They say, 'We're not prisoners; you can't treat us like this.' "

Navy officials say that crews of most merchant vessels, although irritated at the intense searches that can take up to eight hours, have grudgingly come to accept the delay.

"Everyone knows they're going to be stopped," said Capt. James B. Hinkle, commander of the Maritime Interception Forces in the Red Sea. "One ship that transits the area frequently told us it had been stopped eight times in the past three months."

The combination of the interdiction efforts and increased shipping insurance rates brought on by the gulf crisis has slowed sea trade to a trickle in the Red Sea, with merchant shipping down 80 percent since warships began enforcing the U.N. embargo in August, officials said.

Search teams, composed of security units, Navy officers and Coast Guard law enforcement detachments trained in drug interdiction, often are confronted with unpleasant, if not dangerous, situations aboard the trading ships.

When the Sampson's boarding team went to inspect a suspicious merchant ship at 1 a.m. a few weeks ago, members found the rowdy, drunken South Korean crew.

"The crew was drunk as skunks and the master was passed out in his bed," Sullivan said. "I didn't want my guys going inside the skin of that ship with some drunk liable to pick a fight."

After delivering a stern warning about sea safety, the Sampson team left and the ship was allowed to continue.

The team from the missile cruiser USS Biddle has become legendary for its inspection visit to a vessel carrying 5,000 sheep. When the malodorous team returned to the Biddle, the ship's crew ordered them hosed down before they could go below.

The 29-year-old Sampson, scheduled to be decommissioned next year because of budget cuts, conducted the first Red Sea boarding mission Aug. 26. Since then it has painted 30 tanker silhouettes on its gray metal sides, one for each boarding.

"Aditya Kanti? This is Navy warship 10," Sampson skipper Sullivan said into his bridge radio one recent morning, squinting across the calm sea to the massive Indian cargo vessel on the horizon.

He consulted a card hanging nearby and turned on a tape recorder: "In accordance with its previously published notice to mariners, the United States intends to exercise its right to conduct a visit and search of your vessel under international law. Request you stop your vessel and prepare to receive my inspection team. Do you understand me? Over."

"Navy warship, this is Aditya Kanti," crackled the reply. "Is that an American ship? It will take me half an hour to change and stop."

"Looks like a merchant came out and the boss wants us to take a look," boomed the ship's executive officer, Lt. Cmdr. David Birdwell, over the ship's loudspeaker system. "Boarding team, grab a bite to eat and prepare to man the boat soon."

Clad in navy blue coveralls and bright orange lifejackets, the boarding team gathered on the deck. Some nervously puffed cigarettes. Others tried to hide their anxieties with idle chatter, jokes and tales of past adventures ("I swear that rat was as big as a dog").

One leaned over the rail, eyed the hulking tanker drawing nearer and flicked his cigarette butt into the sea. "It's the waiting that's the worst part," he said.

Eventually, the team piled into the Sampson's gray whale boat, hoisted a small, soiled U.S. flag on the stern and bounced across the waves toward the Indian vessel.

One by one the men climbed aboard. They fanned through the ship, some thumbing through its manifest while others searched the holds filled with 2,050 tons of phosphate and 5,250 tons of potash. With the exception of livestock -- and rats -- this fertilizer is perhaps the one most detested by boarding teams. It stinks, it burns open sores, it seeps into the creases of overalls. The Sampson team emerged from about 1 1/2 hours of inspection, coated in the white powder.

"Time to hit the showers," said one weary team member, as he removed the loaded magazine from his pistol.