The pilot of the Korean Air Lines jumbo jet shot down by a Soviet fighter in 1983 radioed incorrect altitude reports to Japanese ground controllers during the flight's final minutes, according to radar data released by the Japanese government.

The data, previously withheld on grounds it would reveal the capability of Japanese military radar, indicates that the Korean jet climbed 3,000 feet just before the Soviet warplane fired the missile that destroyed it.

The Soviet news agency Tass cast the new information as confirming Moscow's contention that the plane was on a spy mission. Japanese specialists called it a significant addition to the small stock of facts on the incident but said it was open to a variety of conflicting interpretations.

The Boeing 747, Flight 007 bound from Anchorage to Seoul, crashed into the sea near Sakhalin Island early on the morning of Sept. 1, 1983, after flying for several hours through Soviet airspace. All 269 people aboard were killed.

Western reconstructions have blamed the incident on a misprogrammed on-board navigational system or other pilot error. However, because the crew was killed and the jet's flight recorders never were recovered, these explanations remain speculative.

At 1:10 a.m. on Sept. 1, after leaving Anchorage, another Korean airliner flying nearby sent a message to controllers that 007 was at 33,000 feet.

Japanese officials say that Flight 007 first appeared on Japanese radar screens at 3:12 a.m., 14 minutes before a Soviet interceptor fired an air-to-air missile at it. The Korean jet was tracked initially by one of three Japanese radar stations on Hokkaido Island.

When radar coverage began, the jet was descending from about 32,000 feet, and traveling at about 430 knots. At 3:15, the radar showed it to be at 29,000 feet.

Controllers never received any message from either Korean plane saying 007 had gone below that altitude. Planes are required to request permission for such changes, unless there is an emergency.

At 3:15 a.m, 007's pilot radioed directly to Japanese controllers asking permission to climb to 35,000 feet. Controllers approved that at 3:19. At 3:20, 007's pilot said he was leaving the 33,000-foot level.

At 3:23, the pilot reported he had reached 35,000 feet. But his actual altitude at the time, according to radar, was 32,000 feet. The missile was fired at 3:26 and Japanese officials say the plane vanished from their radar screens at 3:29.

The data was released by the government to Yutaka Hata, a member of the national legislature who has worked with families of the victims to get more information on the incident. Some relatives charge that the U.S. and Japanese governments have concealed pertinent facts about the jet's downing. Hata said in an interview today that the data proved major discrepancies in the government's accounts. "This will be the start of the real truth-finding," he said.

Hata's group said the descent and climb strengthened theories that the jumbo jet was being flown manually during the final minutes.

According to The Associated Press, Tass reported that in making public the data, the Japanese government "admits that the South Korean aircraft systematically sent ground-based traffic control services deliberately false data about its whereabouts and repeatedly changed altitude, which airliners never do."

Tass said these disclosures "invalidate previous claims by Washington and Tokyo that the South Korean airliner strayed into Soviet airspace due to a mistake in programming its on-board computer."

However, Japanese aviation author Kunio Yanagida, who wrote a book about the crash, said that though the plane may have been under manual control at the end, nothing can be inferred from this information about how it was being flown when it entered Soviet airspace several hours earlier. Altitude discrepancies might be explained by equipment failing or by efforts of the crew of the jet to elude Soviet interceptors, he said.