KUWAIT, JULY 24 -- The first reflagged Kuwaiti supertanker to pass through the Persian Gulf under U.S. Navy protection struck an underwater mine early today, ripping a hole in the ship's hull, setting back Kuwait's oil shuttle and causing some embarrassment to American officials over the penetration of the convoy defenses.

None of the 26 crewmen aboard the 1,200-foot tanker, the Bridgeton, was injured when the explosion, believed to have originated from a World War I-design mine moored to the bottom of the gulf, detonated at 6:50 a.m. (11:50 p.m. Thursday EDT).

The ship took on water but later proceeded to Kuwait at reduced speed from a position 120 miles southeast of Kuwait and about 18 miles west of Farsi Island, which has been used by Iran as a base for speedboat attacks against gulf shipping.

The White House said the United States would not retaliate for the mine attack, and U.S. sources here said the circumstances did not warrant taking action against Iran, the suspected culprit. {Story on Page A21.}

Today's mine explosion prompted an almost immediate comment from Tehran, where Prime Minister Mir Hossein Mousavi called the incident "an irreparable blow to America's political and military prestige.

"The U.S. schemes were foiled by invisible hands," Mousavi was quoted as saying by Iran's news agency. "It proved how vulnerable the Americans are despite their huge and unprecedented military expedition in the Persian Gulf to escort Kuwaiti tankers."

A later Iranian news agency report quoted a military spokesman as saying that Iranian forces carried out "special operations in the gulf" the night before the mine incident. However, Iran did not specifically claim to have placed the mine that damaged the Bridgeton.

The five-ship convoy -- with two warships flanking and one trailing the Bridgeton and a second tanker, the Gas Prince -- was well beyond the halfway point of its inaugural journey when the Bridgeton hit the mine. There was no warship directly in front of the Bridgeton.

The convoy was traveling at about 16 knots when reporters in a press pool on the guided missile destroyer USS Kidd heard a loud boom that rolled over the water from the direction of the Bridgeton, according to pool reports.

"We've been hit! We've been hit!" came the radio report from the Bridgeton, where Navy Lt. Richard Vogel was riding. The distress call crackled over the radio on the bridge of the Kidd, which was trailing the supertanker by about a mile.

Vogel reported that the explosion was so strong that crew members several hundred feet away from the impact were almost knocked down as they stood on the bridge deck. "All of a sudden, the whole ship shuddered and rocked for about 15 to 20 seconds," he recalled. "It actually lifted us off our feet three or four inches."

The Kidd's captain, Cmdr. Daniel J. Murphy Jr., slowed his destroyer to 5 knots and posted sailors with M14 rifles on the bow of his ship with orders to shoot any suspicious objects in the water.

It was soon clear to officers on the bridge of the supertanker, however, that the damage was minor. "The hit is port {left side} amidships, 100 to 200 feet aft of the bow," said one radio report. "There is no danger to the ship, {there is} plenty of reserve buoyancy here."

After the initial damage inspection, the convoy closed ranks to single file, with the Bridgeton in the lead, and the flotilla picked up speed to 10 knots. Murphy, the destroyer captain, told reporters that the mine that hit the Bridgeton was extremely powerful.

"If we had hit that, it would have done enormous damage to the Kidd," the captain said. The huge supertanker is more able to absorb such blows.

Murphy also said he thought the mine was brought from a nearby Iranian island in the predawn hours before the explosion occurred. "We haven't gotten any proof. It's difficult to assess who places a mine. The track record, however, would clearly point the finger to Iran," he said.

The mine attack demonstrated that the United States faces a wide array of threats in its new role as an ally of Kuwait -- and by extension, Iraq -- in the seven-year-old Persian Gulf war between Iran and Iraq. If the mines were laid by seaborne Iranian Revolutionary Guards from one of the many small island redoubts along the gulf, the U.S. Navy could be drawn into a guerrilla war.

Today's incident came two months after the U.S. guided-missile frigate Stark was attacked unexpectedly in the gulf by an Iraqi aircraft, killing 37 U.S. sailors.

Tonight, the Bridgeton was reported by shipping sources to be riding at anchor inside Kuwait's territorial waters. Saturday, it will be inspected by a damage assessment team before it is expected to steam farther south to Bahrain or Dubai for dry-dock repairs.

Though an 18-man U.S. Navy "mine countermeasures team" had conducted extensive mine detection and detonation work over the last two weeks at the entrance to Kuwait's oil loading port, the waters where the Bridgeton was struck had not been searched, U.S. officials said.

The U.S. Navy has about nine warships, none of them mine sweepers, in the gulf. Of the four Soviet warships in the gulf, a senior western diplomat here noted, three are mine sweepers.

"They know what the threat is here," he said.

A western official in Kuwait said one of the serious problems in the U.S. escort operation is the lack of mine-sweeping resources to protect both the American fleet in the gulf and the 11 reflagged Kuwaiti tankers that have become an American responsibility as they shuttle this oil sheikdom's export petroleum products outside the gulf.

Both the Kuwaiti and Saudi Arabian navies have refused to extend their mine-sweeping activities outside their territorial waters. Saudi Arabia last week dispatched two of its American-built mine sweepers to the mouth of Kuwait's harbor channel entrance, 12 miles offshore. This was the area where a mine field was located and cleared after four merchant ships were damaged by underwater mine explosions recently as they entered the channel.

The first mine-damaged ship, on May 16, was the Marshal Chuykov, one of three Soviet oil tankers under charter to Kuwait in a similar protection scheme.

In Kuwait, U.S. Ambassador Anthony Quainton called the incident "a violent act against international shipping" and said "the most likely candidate would have to be the government of Iran or one of its representatives."

Although Quainton said it was "a matter of considerable regret" that the Bridgeton was hit, he added, "I don't think you can characterize the mission as having failed." He added, "I have no reason to suppose that it will lead to any cancellation of our effort to protect tankers that we have reflagged."

When the attack occurred, the 1,050 sailors aboard the three escorting warships were at battle stations under a "general quarters" alert because they were passing through a two-mile-wide choke point near Farsi Island, the suspected base for some of Iran's speedboat attacks against shipping.

Western sources here said the mines recovered in recent mine sweeping operations have been of British World War I design and manufactured in the Soviet Union. A Soviet official here was said by sources to have disavowed any connnection to the mines, known as M08s, saying that a number of M08 mines had been sold to Iran by North Korea.

In a tactic that appeared to put the safety of the Kuwaiti supertanker second to the safety of U.S. warships, the convoy proceeded to Kuwait after the mine went off using the Bridgeton as a plow through the gulf waters in hopes that its massive hull would detonate any additional mines.

Aboard the USS Fox, Capt. William Mathis told reporters that the Kuwaiti supertanker "can take hits easier than we can."

He said, "The Bridgeton will be acting as a deep-draft mine sweeper."

Several hours after the mine explosion, the American convoy passed a small Soviet convoy heading southward. Its composition: two merchant ships escorted by a Soviet mine sweeper.

When the captain of the Kidd radioed to the Soviet convoy the location of the mine that struck the Bridgeton, one of the Soviet merchantmen simply replied: "Thank you, American warship."