KUWAIT, DEC. 7 -- Iranian forces fired a Silkworm missile at Kuwait today but it exploded harmlessly in waters off the main oil loading terminal, the Defense Ministry said.

Shipping sources said the Chinese-made missile hit a decoy barge off Kuwait's Ahmadi offshore terminal at the head of the Persian Gulf.

Officers of the state-run Kuwait Petroleum Corp. said the missile landed in the water halfway between the terminal and a floating mooring for supertankers. Maritime executives in the gulf said the missile's radar was deflected successfully by a decoy barge deployed about a mile south of the Sea Island terminal, and it hit the barge.

About 10 small platforms, with metal grids to deflect missiles, have been spotted through the terminal area's waters as part of Kuwait's defenses, said the executives, who spoke on condition of anonymity.

Iran did not acknowledge firing the missile, the seventh reported to have hit Kuwait's waters or territory this year. Three launched in October hit two tankers and a loading dock.

Iran accuses Kuwait of supporting Iraq in the seven-year-old war. The Silkworms have a range of about 50 miles and are believed to be fired from captured territory on Iraq's Faw Peninsula.

Kuwait protested today's attack to the Iranian charge d'affaires. Sabah Ahmed Sabah, the foreign minister, sent messages to international, regional and Arab organizations about the "aggression," the Kuwait News Agency reported.

The missile fired today apparently was aimed at the terminal's Sea Island facility for loading supertankers. It resumed partial operation 10 days ago after being seriously damaged in a Silkworm strike Oct. 22.

Among ships served by the terminal are some of the 11 Kuwaiti tankers given U.S. registration and American flags last summer so U.S. Navy escort ships could protect them.

Lloyd's Shipping Intelligence Unit of London confirmed an Iraqi air raid that badly damaged a Cypriot-flag tanker near Iran's huge Kharg Island oil terminal in the northern gulf. It said the 238,909-ton Actinia was fully loaded from Kharg when attacked twice within five hours Friday.

Iraqi planes hit the same tanker in September in the air campaign against the oil exports with which Iran finances the war. The Actinia is one of several tankers the Iranians use to ferry oil from Kharg to makeshift terminals in safer waters about 450 miles down the gulf.

At the lower end of the gulf, a Singapore-flag tanker with a load of naphtha from Saudi Arabia was reported sinking after a fire burned it "from end to end" despite efforts by salvage tugboats. The ship was hit yesterday by rocket-propelled grenades fired from Iranian speedboats.

Salvage agents said fire was ravaging the 85,129-ton Norman Atlantic, the Singapore-flag tanker adrift in the Strait of Hormuz.

An Omani Navy officer whose gunboat rescued the 33 crewmen said the tanker "is burned from end to end."