KUWAIT, AUG. 11 -- The second U.S.-escorted convoy of reflagged Kuwaiti ships arrived here today late but unscathed after dodging at least one new mine and being shadowed for most of its journey through the Persian Gulf by an Iranian frigate.

In the Gulf of Oman, south of the Persian Gulf, four more mines were discovered today in the same area where a U.S.-chartered supertanker hit a mine yesterday.

The three Kuwaiti ships flying the Stars and Stripes -- two tankers and a liquefied-gas carrier -- and their four Navy escorts reached Kuwaiti territorial waters this afternoon after a voyage through the 550-mile-long gulf that lasted almost four days, according to Kuwait shipping sources.

"They are safe and sound and at anchorage waiting for berths so they can begin being loaded with oil and gas," said one senior Kuwaiti shipping official tonight. "As soon as they are loaded they will head out again."

The convoy completed its voyage as evidence grew that the hazards the U.S.-escorted ships face in the gulf are growing rather than decreasing. In the skies over the convoy last weekend, U.S. jet fighters fired two missiles at an Iranian warplane that approached a U.S. P3 reconnaissance plane, but the missiles missed their target.

U.S. helicopters preceding the convoy today spotted at least one new mine on a shipping route leading to Kuwait, and Omani mine hunters called in to sweep the previously untroubled Gulf of Oman off Fujayrah discovered four new mines anchored to the sea bottom in what is a normally busy ship staging harbor.

{Administration sources in Washington said Tuesday that Kuwait and Saudi Arabia in recent days have been quietly assisting in mine-sweeping operations for the U.S.-escorted convoy, Washington Post staff writer Molly Moore reported. The sources said one mine had been detected near the path of the convoy in the northern Persian Gulf.

{NBC News reported that the helicopter carrier USS Guadalcanal, which is carrying eight Sea Stallion mine-sweeping helicopters for use in the gulf, has broken down with electrical problems at the Indian Ocean island of Diego Garcia.}

The new mines found off Fujayrah outside of the Persian Gulf ended any hopes that the mine that holed the 117,200-ton Texaco Caribbean yesterday was a haphazard accident caused by a mine that had somehow drifted from the Persian Gulf.

The Omani mine hunters, shipping sources here said, established the mines were the same type as the mines of North Korean design that previously had been found in shipping lanes inside the Persian Gulf. While the source of the mines off Fujayrah remains unknown, U.S. officials have said they believe the Persian Gulf mines were laid by Iran to try to hamper the U.S. convoys to Kuwait.

A similiar mine damaged the 401,382-ton reflagged supertanker Bridgeton July 24 during the first U.S. Navy convoy. Although this week's convoy followed a different path -- farther away from the Iran's Farsi Island, close to where the Bridgeton was hit -- Kuwaiti officials said it was forced to halt off the Saudi Arabian coast for at least a day after U.S. helicopters spotted a new mine in its path. The convoy resumed its journey after the mine was charted and a route around it found.

Sources close to the U.S. Navy convoy operations said that it is believed that Iranian Revolutionary Guards are using four Chinese-supplied trawlers to lay the mines in the shipping lanes. One such trawler was spotted preceding the U.S. convoy three days ago before the new mine was found.

{Iran's speaker of parliament, Hojatoleslam Ali Akbar Hashemi Rafsanjani, said the mine that damaged the Texaco Caribbean was planted "by the United States or its allies, if not by Iraq" and said Tehran had ordered its Navy to clear the area of mines, Agence France-Presse reported.}

Although the sudden proliferation of mines in the shipping channels has alarmed many government officials, who fear Iran is seeking to isolate Kuwait, shipping authorities here are dismissive of the mine threat.

"Frankly, the mines are at most a nuisance to our shipping," said one Kuwait shipping official. "They haven't even put a dent in the flow of shipping through the gulf. They haven't affected a thing. Our {deliveries} are being met."

The sources said the types of mines that have been encountered do relatively little damage to tankers, and what damage they do inflict is quickly repaired. The most significant threat they pose is to the U.S. Navy vessels now plying the gulf because their hulls are relatively thin compared to the tankers and could be more severely damaged.

While world attention has focused on the U.S. convoys, it has been noted here that on any given day, half a dozen other ships may be plying the gulf to and from Kuwait without incident.

Among these ships are three Soviet tankers that have been chartered by Kuwait, which are being escorted by three Soviet mine sweepers with little fanfare or publicity. It was on May 17, before the U.S. convoys began, that the chartered Soviet tanker Marshal Chuykov became the first ship in the gulf to strike a mine.

The Soviet Union made no issue of that incident, however, and the 37,400-ton tanker was quickly repaired and put back in service.

Shipping sources said that about 70 tankers come to Kuwait monthly. Last month, 68 vessels shipped 14.37 million tons of crude oil from the gulf to the West, compared with the 20 vessels that plied the gulf in April, The Associated Press reported from London.

Sources here said Kuwaiti-owned ships have barely been touched by the "tanker war" that began in 1984 between Iran and Iraq, in which 330 tankers have been hit by air strikes, sea attacks or, since May, mines.

An official of Kuwait's national line, the Kuwaiti Oil Tanker Co., said that only six attacks have been made against its 22-ship fleet since 1984.

It was because of Kuwaiti concerns about the threat of Iranian attacks on its oil-tanker traffic that Kuwait requested, and the United States agreed, to reflag 11 of the 22 ships and provide them with the escorts that constitute a major U.S. military buildup in the area.

Tensions in the area increased further yesterday when Iraq resumed its air attacks on Iranian oil facilities for the first time in 25 days. The Iraqis, under pressure from the Washington and other members of the United Nations Security Council, had suspended air raids on Iranian oil facilities shortly before the council passed a resolution on July 20 calling for a cease-fire in the seven-year-old Persian Gulf war.

Iraq said yesterday it had resumed the attacks because Iran had refused to accept the cease-fire resolution.

Iran warned last month that it would retaliate against any further Iraqi attacks on its vital oil industry, even if it meant hitting Kuwaiti oil facilities as well. Iran considers Kuwait an ally of Iraq because it has provided port facilities and cash subsidies to Iraq.