Investigators said today that a KLM jumbo jet was not cleared for takeoff when it sped down the runway and slammed into a Pan American jumbo jet Sunday in aviation's worst disaster.

They said that a tape recording of control tower communications also showed that the Pan American plane had missed a turn that would have taken it off the runway and out of the KLM plane's path.

The announcements by Dutch and Spanish officials investigating the disaster that killed 575 persons were made as 65 to the 71 survivors left the island on a U.S. Air Force hospital plane.

They were expected to arrive at McGuire Air Force Base, N.J., late tonight and several were to be flown to the U.S. army burn treatment center in San Antonio, Tex.

Franz van Rejsen, head of the investigating team from the Netherlands, said taped conversations between the control tower and the two planes showed that the KLM pilot had been given preliminary clearance but not final takeoff permission.

"But the KLM plane started, which is not in accordance with normal procedure." Van Rejsen said. "We presume there was a misunderstanding in the KLM cockpit regarding the position of the Pan American plane on the runway."

Earlier Juan Linares, deputy director of Santa Cruz airport, told reporters that the Dutch plane "did not receive clearance from the control tower to take off."

In Amsterdam, a KLM spokesman said it would have been "completely unthinkable" for the pilot to have started his takeoff without proper clearance. The spokesman said KLM would withhold further comment until it had examined the recorder that tapes cockpit conversations as well as radio communications.

Van Rejsen said visibility at the time of the crash was 300 yards because of ground fog. He said the Pan American 747 had taxied farther along the runway than it had been authorized.

"The Pan American plane missed the third turning off the runway," he said, apparently referring to the taxi lane the U.S. plane was to take in preparation for its takeoff behind the KLM plane.

W. H. Waltrip, the Pan American executive vice president in charge of operations, said the American plane had been correctly carrying our control tower instructions and that it Van Rejsen had said otherwise, "he will have to justify it."

Douglas Dreyfus, head of a U.S. National Transportation Safety Board team here, said the Spanish government had agreed to allow the flight recorder and cockpit voice recorder from the Pan American jet to be taken to the United States for examination.

Dreyfus said he understood the flight recorder from the KLM plane had not been found. A KLM spokesman said the cockpit voice recorder from the Dutch plane had been impounded by Spanish authorities.

According to persons who heard the radio tapes, the Pan American pilot shouted, "We are still on the runway" as he saw the KLM barrelling down on his own jampacked 747 jumbo jet. His warning came too late to stop the 400-ton Dutch craft, rushing down the runway at 186 miles an hour.

The Madrid newspaper Pueblo said the tapes showed that the Pan American pilot yelled, "This man is crazy. What's he doing? He'll kill us all!" There was no official confirmation.

An air traffic controller on duty at the time of the crash told the Toronto Star in a telephone interview: "Nobody knows how the KLM captain could make such a stupid mistake."

Van Rejsen told a press conference that the KLM pilot had been given only "flight clearance. He should now have asked for takeoff clearance, which he did not."

Instead, according to Van Rejsen, the Dutch captain merely said, "we are taking off," and started the fatal takeoff run.

The KLM pilot, Capt. Z. A. Vedhuizen van Zanten, 50, was killed in the collision, along with the other 248 persons aboard the KLM jet.

Van Zanten, according to a KLM spokesman in Amsterdam, "was our chief instructor for other jumbo jet pilots." In this role, he had been featured in a KLM advertisement, "but we decided to withdraw the ad now," the KLM spokesman said.

Capt. Victor S. Grubbs, the pilot of the Pan American plane, survived the collision. He was among those flown from here today.

An American Air Force C-130 cargo plane, the first fixed-wing craft to land at Santa Cruz airport since the collision, flew 65 of the 71 survivors 65 miles to Grand Canary Island, where a larger C-141 jet starlifter medical evacuation plane waited to take most of them to the United States.

Some of those on the mercy flight were bound for Brooke Army Medical Center at Ft. Sam Houston in San Antonio, Tex., a six-hospital complex that has a world-renowned unit for treatment of burn injuries.

A Pentagon spokesman said in Washington that 10 of the survivors being returned to the United States are seriously burned while 20 others require hospitalization for unspecified injuries. The rest are ambulatory, he said.

Those flown from here today included 28 stretcher patients, officials said. Six survivors, all Americans, were too critically injured to be moved from Tenerife.

Initially Spanish medical authorities opposed evacuation of even the less seriously injured. "I was against their being moved," said Tenerife Hospital Director Eusebio Gambin, "but when the Americans said they would take full responsibility, I said okay. This is bad, bad."