DUBAI, UNITED ARAB EMIRATES, SEPT. -- Using specially trained Coast Guard officers, shipping intelligence and sophisticated radar and communications technologies, U.S. and allied naval forces have dropped a net over sea traffic in Middle East waters that independent shippers say is nearly impossible for large vessels to evade.

The effort by U.S. and European warships to enforce U.N. economic sanctions against Iraq in the Persian Gulf and the Red Sea has transformed the region's sea lanes into a virtual police state. Warships challenge commercial vessels dozens of times each day, filling maritime airwaves with interrogations that are alternately tense, humorous and hostile.

Commercial shippers say the intelligence about shipping movements and the technologies possessed by U.S., British and French warships, combined with international support for sanctions against Iraq, have created an unprecedented blockade of Iraqi and Kuwaiti ports in the northern gulf and the Jordanian port of Aqaba off the Red Sea, through which Iraq has tried to move supplies in recent weeks.

"I can't imagine a big ship ducking and diving through the dragnet," said a senior manager at shipping giant Gray Mackenzie Group, who asked not to be named. "There are too many eyes and ears. The noose is there and it's pretty bloody tight."

Israeli official sources said today that Iraq continues to receive shipments of food by air from Yemen, Jordan, Libya, Tunisia and Sudan, Washington Post correspondent Jackson Diehl reported from Jerusalem. The Israelis said ships are delivering cargos of food to ports in these countries and the goods are then flown to Iraq in commercial airliners.

Official sources said they could not say how much contraband was being sent that way or how often the flights were. One official said: "I don't think this is any dramatic loophole in the embargo. But it sheds light on the positions of the governments involved."

According to U.S. Navy officers and commercial shippers, the naval operations now underway to shut down Iraqi imports and exports depend on a number of components: radar and satellite photos to track shipping movements, intelligence and public records about the ownership and destinations of commercial vessels, and coordination among U.S. and allied warships to shadow vessels suspected of running the blockade.

So far, partly because Iraqi-flagged vessels reportedly have been instructed by Baghdad not to resist ships enforcing the blockade, Western warships have not resorted to force to disable any commercial vessels. Two U.S. warships fired warning shots past Iraqi ships Aug. 18, but no shots have been fired since by U.S. or European ships, according to a U.S. Navy spokesman.

Boardings and inspections of suspected blockade-runners have been infrequent, numbering less than a dozen so far, according to officials. Commercial shippers say they believe that is because naval intelligence and tracking devices render first-hand inspections largely unnecessary.

They also say shipping traffic in the gulf and Red Sea has diminished considerably since Iraq's Aug. 2 invasion of Kuwait, mainly due to soaring insurance rates.

Dozens of officers from the U.S. Coast Guard, trained in boarding and inspecting commercial vessels suspected of smuggling drugs and other contraband into the United States, have recently been deployed on Navy warships in the gulf and Red Sea to carry out boarding and search operations when they do occur, a Navy spokesman said last week.

"Those are the guys who are actually doing the boarding and inspections now," said Lt. Cmdr. Ron Morse. "They're a lot more familiar with what a commercial destination manifest looks like and where you try to hide things in a merchant ship."

The vast majority of challenges have involved only interrogations conducted over maritime radio. Warships initiate the interrogations by identifying themselves to a commercial vessel. Then they question the ship's captain about his registry, cargo, destination and last port of call.

The opening of a naval interrogation -- "This is U.S. Navy warship channel one-six" -- has become a kind of repetitive jingle on the region's main maritime radio frequency.

The conversations that follow generally consist of businesslike exchanges of information, but there are interjections of tension, such as the instance Friday when an unidentified commercial ship captain near Dubai responded to persistent inquiries from a U.S. Navy frigate by saying again and again, "I cannot give you this."

It was not clear how the Navy warship ultimately responded to the captain's defiance. Navy officials have declined to discuss specific operations.

The interrogations are also punctuated by angry radio operators and pranksters who break into conversations to berate the U.S. military presence in the gulf, shout random strings of expletives or sing songs. "Go back to your country, Yankee {expletive}" is an occasional refrain on the main maritime channel here.

U.S. Navy technicians generally handle the interrogations in a by-the-book tone of neutrality, while radio operators on British warships frequently joke and laugh with commercial ship captains. "We all have different ways of doing things," said a British diplomat in the gulf. "It's not that we take it as a joke, it's that we think if it can be more relaxed and pleasant, there's perhaps less likelihood of a nasty misunderstanding."

Commercial shippers here say that after years of tension in gulf sea lanes during the Iran-Iraq war, merchant vessels' captains have grown accustomed to military protocol. "A captain who's worked in the gulf for the last 10 years is well used to this and probably glad that he's not talking to someone {on an Iranian or Iraqi warship} who's likely to put an Exocet missile through his engines," one shipping company manager said.

U.S. Navy officers say the radio interrogations are adequate in most cases because warships patrolling the gulf have vast stores of computer data about commercial vessels as well as access to intelligence -- ranging from surveillance by radar aircraft and satellites to publicly available port records -- with which to identify ownership, cargo loads and routes of specific ships.

Three types of large commercial ships ply the Middle East waters under surveillance by Western warships: oil tankers, bulk cargo ships that carry large stores of grain or other produce, and container ships that carry diverse cargo in individual crates.

Shippers say the latter are the most difficult to monitor because of the variety of cargo on board but they add that war-risk insurance premiums and adherence to U.N. sanctions have driven most large container ships out of the Persian Gulf and away from Iraqi and Kuwaiti ports.

Such ships do continue to operate in the Red Sea near the Jordanian port of Aqaba, they said. That is where most of the U.S. Navy boardings and inspections of merchant vessels have occurred, including an instance in which a vessel registered in Sri Lanka and carrying chemicals apparently bound for Iraq was turned away.

Traders and bankers in the gulf region say smugglers using traditional wooden sailboats called dhows are seeking to profit by moving goods into Iraq by sea and land.

But these smaller vessels, which are generally ignored by Western naval forces, are considered unable to carry enough cargo to open a major breach in Iraq's economic isolation.

Oil tankers and the single-load bulk cargo ships pose relatively few problems for the naval forces, partly because Iraqi and Kuwaiti ports lack the facilities to load or unload the giant vessels.

Large oil tankers continue to travel in the northern gulf -- near Iraqi and Kuwaiti oil terminals -- to deliver and take on loads at the Iranian terminal at Kharg Island. But shippers and Navy officials say they see no evidence that Iran is helping Iraq evade sanctions by shifting Iraqi or Kuwaiti oil into its tankers or by selling its oil for Iraq's account. U.S. Navy ships have no orders to harass or detain Iranian oil tankers, spokesman Morse said.

Iraq maintains a small fleet of state-owned oil tankers to export some of its petroleum products, but before the invasion it also chartered commercial tankers. The state-owned Iraqi tankers are prominently marked and several have already been identified and shadowed by U.S. warships.

Kuwait maintained a larger fleet of tankers than did Iraq, but the Kuwaiti ships have been idled since the invasion, according to commercial shippers.