KUWAIT, AUG. 15 -- An explosion ripped through a showcase Saudi Arabian natural gas plant on the Persian Gulf today, and a mine in the Gulf of Oman sank a supply ship off the United Arab Emirates port of Fujayrah.

The mine sank the supply ship Anita, killing at least one of its crewmen and injuring five, according to sources in the Gulf Agency Co., which owns the ship. Five other persons, including the ship's captain, were missing and presumed dead.

Gulf Agency officials said the Anita struck a mine three miles off Fujayrah and sank immediately. Coast Guard vessels and helicopters hunted for the missing crewmen until nightfall, but hopes were not high that they would find any of them alive.

Another mine found about 180 miles northwest of Ras Tannurah killed a Saudi frogman Wednesday and wounded another as they sought to defuse it, the official Saudi Press Agency (SPA) reported today.

There were conflicting reports on casualties and the circumstances of the gas plant explosion in Saudi Arabia. The government reported that early this morning "a fire broke out" at the Juaymah natural gas complex on the Persian Gulf, about 10 miles north of Saudi Arabia's main oil-export facility at Ras Tannurah.

The SPA attributed the fire and explosion to an unspecified electrical failure, but recent tensions between Iran and Saudi Arabia left open the question of sabotage. Iran has threatened to retaliate for the deaths of at least 275 Iranian pilgrims during a clash with Saudi police in Mecca on July 31.

Although Saudi Arabia only mentioned a fire at the plant, which was completed in 1980 as a model of the government's economic diversification, witnesses reported that the fire was preceded by an explosion that was heard six miles away.

Western diplomats reached by phone in the Saudi capital tonight said they remained dubious of the Saudi account that the explosion was not the result of Iranian-inspired sabotage.

"Security around the plant is very thin," one diplomat reported. "It is very vulnerable to sabotage."

Saudi Arabia reported that only four workers were injured at the gas plant, but diplomats in Riyadh, the Saudi capital, said the toll could be as high as 22 dead and 15 wounded.

{Although several Americans work in and near the plant, none was injured in the incident, a State Department spokesman told United Press International.}

Twelve hours after the explosion, fires were reported still burning at the plant, although they were said to be under control.

Sabotage was suspected in an explosion on May 22 in a propane gas storage tank at a vital gas installation in Kuwait. Kuwaiti police said the blast was orchestrated by a Kuwaiti Shiite Moslem, Faisal Ahmed Karam Neiruz, who they suspect has links to Iran.

Iran has repeatedly threatened to attack Saudi and Kuwaiti oil and gas facilities because of the two nations' support for Iraq in its seven-year-old war against Iran.

The oil-rich region in which today's explosion occurred, known in Saudi Arabia as the Eastern Province, is heavily populated by Shiites, who make up much of the work force in the oil and gas industry there. Both Saudi Arabia and Kuwait have Sunni Moslem majority populations. Iran has a Shiite majority and has encouraged Shiites in neighboring Arab gulf states to rise against their rulers.

Iran is also believed by western governments to be behind the placement of mines found recently in Persian Gulf shipping lanes and, farther south, around the main shipping anchorage off Fujayrah on the Gulf of Oman.

Today's sinking of the 156-foot Anita came little more than a day after the United Arab Emirates lifted a two-mile danger exclusion zone off its coast and proclaimed the area virtually clear of the mines that had been spotted there earlier in the week.

The exclusion zone had been ordered after the U.S.-operated, Panama-registered supertanker Texaco Caribbean struck a mine off Fujayrah last Monday. In the intervening days, UAE coast guardsmen aided by Army helicopters spotted another three mines, two of which were defused and a third of which they lost track.

Officials of the UAE, whose commerce depends on the security of its waters, have been shocked and defensive about the mines that appeared there Monday. It was the first time that mines -- or other dangers related to the Iran-Iraq war -- had appeared in the Gulf of Oman.

Shipping officials interviewed by telephone today were openly critical of the UAE government for prematurely proclaiming the Fujayrah anchorage waters mine-free. Yesterday, when a ship captain notified them that he had spotted a mine floating nearby, the UAE dismissed it as the hump of a bloated dead camel.

But today, after the Anita was blown up, Fujayrah port officials imposed a new exclusion zone in the waters off Fujayrah and the port of Khor Fakkan to the north, extending 10 miles offshore.

The Anita was the seventh ship to have struck a mine in the region since the first mines began to appear last May.

Journalists flying over the area today reported spotting two additional mines between Fujayrah and Khor Fakkan, the small UAE port whose waters have been used as a staging area for U.S. Navy-escorted convoys of reflagged Kuwaiti tankers.

Today's incidents came as the U.S. Navy was preparing to escort a new convoy of three Kuwaiti vessels through the Persian Gulf. Iran for a second day continued its naval mine-sweeping operations in international waters beyond the Strait of Hormuz.

The proliferation of mines has prompted a mobilization of mine-hunting vessels and helicopters from the United States, Britain and France. Most of the mine-hunting ships, however, will not be in the area until the end of the month. A U.S. ship carrying eight Sea Stallion mine-sweeping helicopters is expected to reach the gulf area within the next few days.