KUWAIT -- Despite U.S. convoy protection that has provided security for nine of the Kuwait Petroleum Corp. oil tankers registered under the American flag, Iran continues to inflict heavy damage on unprotected shipping bound to and from Kuwaiti ports, according to officials here.

These attacks pose special problems for Kuwait, which more than any other Arab oil-producing nation has built an integrated state industry that competes in world markets with such multinational giants as Shell, Exxon and British Petroleum.

Government figures made available by sources here show that since the U.S. convoy operation began last summer, 16 merchant ships carrying oil or cargo to or from Kuwait have been attacked by Iranian gunboats patrolling the entrance to the Persian Gulf.

The accounting does not include the serious damage done to two of the reflagged tankers -- the Bridgeton, which hit an Iranian mine July 24, or the Sea Isle City, struck by a Silkworm missile Oct. 17.

"We're still getting hit pretty hard," said a government official here, "and now it is all from {Iranian} frigates."

Kuwait critically depends on the U.S. Navy convoys to export liquefied natural gas for Japanese customers and refined petroleum products such as naphtha and gasoline for its refineries and "Q8" service stations in Europe, the official said.

"The Americans have certainly assisted in getting the {refined} products and the gas out, all of it," he said. "It was critical to get the products out to supply our downstream operations in Europe."

"On the crude oil side," the official said, "it has been done without the Americans."

Iranian attacks on oil tankers sent by customers or chartered by Kuwait to meet its contracts abroad inflicted millions of dollars in damage on Kuwait's oil commerce last year and have left the conservative ruling family here concerned that Iran could easily escalate its aggression against Kuwaiti targets.

During last week's visit of U.S. Defense Secretary Frank Carlucci, a high Kuwaiti official expressed appreciation for what he characterized as Carlucci's private assurances "that the United States would help Kuwait if the war expands."

Kuwaiti officials are pleased with the convoy operation, but concern remains about the future.

The Iranians sank a supertanker carrying a full load of volatile naphtha from Kuwait on Dec. 6 and Iran's extensive intelligence network targeted a quarter of the vessels calling on Kuwaiti ports during the month, officials here said.

The attacks were so intense in December that the sheikdom was in danger of not being able to meet its contracts to deliver crude oil to customers in Europe and the Far East.

Three of those attacks, between Dec. 18 and 23, virtually disabled Kuwait's crude oil fleet of chartered supertankers, the official said. "We got hit really bad over Christmas," he said. All of the attacks occurred within a few miles of each other off the United Arab Emirates in the southern gulf.

On Dec. 18, an Iranian frigate, under surveillance by U.S. and British warships, pumped four-inch artillery shells into the Norwegian-registered Happy Kari and set the 290,762-ton vessel's starboard fuel tank on fire as it headed fully loaded out of the waterway.

On Dec. 22, a Liberian-registered supertanker, the Stena Concordia, was hugging the coast of Dubai bound for Kuwait when the Iranian frigate pumped 15 artillery shells into the 273,712-ton vessel and raked the crew's quarters with heavy machine-gun fire.

The following night, the frigate spotted the Norwegian-registered Berge Big, also bound for Kuwait. The Iranians scored seven hits on the 285,400-ton vessel with rocket-propelled grenades, setting its starboard fuel tanks on fire.

There were no injuries to crew members aboard the tankers, but all three suffered damages that rendered them unfit for hauling Kuwaiti crude oil under contract.

As a result of these attacks, U.S. Navy and Kuwaiti Oil Ministry officials were forced to reverse their decision last fall to keep the Bridgeton, the largest of Kuwait's supertankers, outside the gulf after six weeks of repairs in a shipyard.

Regarded as a high-profile target that symbolizes the first Iranian "victory" over the reflagged Kuwaiti tanker fleet, Bridgeton swung at anchor off the Gulf of Oman port of Khor Fakkan for two months before being called back for what is expected to be temporary convoy duty.

"We had been getting our crude oil out without the Bridgeton and if we can live without her, we prefer to keep her outside the gulf," said a senior official in Kuwait's oil and shipping administration.

On Dec. 29, the Bridgeton reentered the gulf and made the 36-hour transit to Kuwait's crude oil loading port at Ahmadi. After taking on a load of crude, the 401,382-ton ship was escorted back out of the gulf by U.S. warships and mine sweepers.