Two American-owned supertankers collided and exploded in flames off the coast of South Africa this morning, spreading a three-mile oil slick near popular resorts, authorities here reported.

Two seamen were reported missing and 82 others were rescued by a helicopter and two ships that rushed to the scene. Most of the crewmen were Chinese, South African maritime authorities said.

The ships, both owned by a subsidiary of Bethlehem Steel in Baltimore, collided about 60 miles west of Port Elizabeth, according to Sonny Manson, an assistant manager of the parent shipping company's Cape Town agency.

Authorities are pessimistic about finding the two missing crewmen in the shark-infested waters.

The helicopter landed on the deck of one of the burining vessels to pick up 13 of the stranded sailors. Dozens of others leaped to safety into the waters of the Indian Ocean.

The Venoil, with a cargo of between 1.4 million and 1.7 million barrels of crude oil, was on it way to Europe and its sister ship, the Venpet, which was in ballast, was headed for the Persian Gulf, Manson said. The half-mile wide slick was caused by bunker fuel oil and diesel fuel from the Venpet, authorities said.

The cause of the collision, which officials described the worst ever along South Africa's coastline, was not clear. Although there was slight fog at the time of the accident, Ian Simpson, assistant port captain at Port Elizabeth and coordinator of the rescue operation, estimated the visibility at about two miles.

The passage around South Africa's Cape of Good Hope is extremely busy since it is used by all tankers traveling between Europe and Americas to the oil countries in the Persian Gulf.

According to Simpson, the Venpet was hit about 300 feet forward of its stern on the starboard side and was sliced right back to its stern. The crew accomodation there was set afire.

[SOURCE OMITTED FROM TEXT] 70 feet along its bow, which began to burn, Simpson said. As of early this evening, the fire had not spread to the cargo tanks of the Venoil, he said.

The two abandoned ships were about two miles apart and drifting in an easterly direction. Neither appeared in danger of sinking.

Port authorities believe the Venoil's cargo will not be lost if the weather does not change and the fire does not spread to the ship's cargo holds.

A small tug rushed immediately to the stricken vessels and by afternoon it was fighting the fire on the Venpet. A larger government tug was dispatched from Cape Town.

The 300,000-ton ships were commissioned in 1973 and according to the South African Press Agency are insured for about $64 million.

According to eye witnesses, flames reached up to 200 feet in the air and smoke billowed up to 1,000 feet shortly after the collision this morning. The sea around the vessels was also ablaze for some hours with burning oil. Lifeboats and rafts littered the sea at the scene.

A supertanker is considered to be a vessel or 300,000 tons or more. The Argo Merchant which ran aground and broke up off Nantucket last December was carrying 7.5 million gallons of oil. Officials said the collision would have been "a major disaster" if both vessels had been fully loaded with oil.