Canadian and U.S. officials yesterday launched investigations to determine why a Delta Air Lines jumbo jet drifted 60 miles off course over the North Atlantic and came within 100 feet of colliding with a Continental Airlines jet Wednesday.

The U.S. planes involved in the near-collision carried almost 600 passengers and crew members. It happened in Canadian airspace near Newfoundland. The planes passed close enough to one another that many of the 399 passengers and 25 crew members on the Continental Boeing 747 said they could read the numbers on the Delta jet's tail.

The Delta L1011-500 Tristar, which had left London three hours earlier with 167 passengers and crew aboard, was headed for Cincinnati when the incident occurred in clear skies shortly after noon. An American Airlines jet in the area helped guide the errant Delta flight by radio back to a safe course, authorities said.

Christiane Beaulieu, spokeswoman for the Canadian Aviation Safety Board, said the Delta plane passed underneath the Continental aircraft. "They were very lucky. One hundred feet is very little," she said.

It was the third time in eight days that a Delta flight was involved in a potentially dangerous in-flight mishap, which a spokesman for the airline blamed on "lady luck."

On June 30 a Delta flight crew, heading for Cincinnati from Los Angeles, inadvertently turned off its jet's engines. The engines were restarted in time to prevent a crash, and the flight continued without further difficulty. Delta announced yesterday that the captain of that jet had been grounded.

And on Tuesday a Delta flight landed at the wrong airport in Kentucky during severe thunderstorms.

A Delta spokesman swiftly rejected any suggestion that the incidents were connected. "When you have human beings you are going to have this kind of occurrence. And we are checking to see if we need changes in procedures or training," said Delta spokesman Bill Berry.

Jim Ewing, director of national media relations for Delta said, "We are talking about three different planes and three different crews. We are satisfied there is no link."

He said the near-collision on Wednesday was "extremely extraordinary, quite remarkable. We are all very upset about it, as you can imagine."

The Canadian Aviation Safety Board announced that it will investigate the near-collision. The Federal Aviation Administration here said it will conduct an inquiry even though the incident did not occur in U.S. airspace. A spokesman for the FAA said, "This was an American flight crew. And we want to know why it happened."

The Continental crew, bound from London to Newark, immediately reported the incident to the Canadian authorities.

The incident was witnessed by the crew of an American Air Lines Boeing 767 that was flying from Paris to Chicago. It was 10 miles behind and 4,000 feet above the other planes. American spokesman Steve McGregor said, "Our flight crew saw the Delta plane pass close to the Continental plane. Delta then indicated its intention to return to its original course over the radio frequency. Continental had meanwhile lost sight of the Delta jet so the American Air Lines crew indicated that it had both planes in sight and could come to Delta's assistance."

Delta Air Lines officials were yesterday interviewing the three-member crew. "We have no idea what happened as yet," Ewing said. "We say with a great deal of confidence that we have the newest and safest aircraft fleet in the world."END NOTES

Planes flying over the Atlantic have no radar guidance because the curvature of the Earth prevents land radar stations from following their progress. They are required to keep 60 miles apart horizontally and 2,000 feet vertically, the FAA said.