The Soviet Union charged yesterday that the South Korean airliner downed in the Sea of Japan Thursday morning (Wednesday afternoon, EDT) had been sent over its territory on a "preplanned" intelligence mission.

The Soviet statement, issued by the official Tass news agency, was Moscow's fullest reaction so far to the international storm set off by charges that the Korean Air Lines plane, with 269 people aboard, was shot down with a missile fired by a Soviet fighter. The statement did not respond directly to the charges made by the United States and other governments but said for the first time that "a Soviet aircraft fired warning shots and tracer shells along the flying route of the plane" as it crossed the Soviet island of Sakhalin.

As in their statement Thursday, the Soviets yesterday maintained that the plane ignored their warnings "and continued its flight toward the Sea of Japan." The plane was tracked for "about 10 minutes" after leaving Sakhalin and then "could be observed no more," Tass added.

Early today in Tokyo, Japanese Foreign Minister Shintaro Abe told reporters that the Soviets had found some wreckage from the plane, United Press International reported. Abe, who met with Soviet Ambassador Vladimir Pavlov this morning, quoted Pavlov as saying the wreckage had been found in Soviet waters near Moneron Island, about 42 miles southwest of Sakhalin.

Abe said the Soviet ambassador said "he had no idea" if the Soviet search vessels had recovered any bodies among the wreckage. Last night, Reagan administration sources told The Associated Press that the United States had learned that the Soviet searchers had found some bodies, but the account could not be confirmed.

U.S. and Japanese search efforts also continued, but government sources in Tokyo and Washington charged yesterday that Soviet officials had refused to allow U.S. and Japanese search ships to enter Soviet territorial waters within 12 miles of Sakhalin, close to the area where a Japanese patrol ship found a 100-yard-long oil slick yesterday morning.

In Moscow's first concession to the international outcry for an apology, yesterday's statement said, "Tass is authorized to state that, in the leading circles of the Soviet Union, regret is expressed over the loss of human life." But the statement concluded by condemning "those who consciously or as a result of criminal disregard have allowed the death of people and are now trying to use this occurrence for unseemly political aims."

It singled out "the impudent, slanderous statement in respect of the Soviet Union that was instantly made by President Reagan."

The first reaction suggested that the Soviet statement had done little to blunt international outrage over the incident. Some observers viewed it as an attempt at damage control, intended to give western Communist parties an agreed line of defense against attacks. Its belligerent tone seemed to rule out any intent to issue an apology, at least for the time being.

In Moscow, a U.S. Embassy spokesman told AP, "It's hard to believe that anybody anywhere could believe this preposterous statement, much less of course those who concocted it."

In Western Europe, Soviet ambassadors in at least four countries were called to foreign ministries and asked to provide a full explanation of the plane's disappearance. But political leaders also expressed hope that the incident would not jeopardize moves to improve East-West relations.

At the United Nations, U.S. Ambassador Charles M. Lichenstein attacked the Soviet Union for "wanton, calculated, deliberate murder" before a special meeting of the Security Council.

In Seoul, South Korean Foreign Minister Lee Bum Suk demanded that the Soviets apologize for their action, pay compensation for all losses and guarantee that no such event will happen again.

In Tokyo, the Japanese Foreign Ministry announced that Japan's ambassador in Moscow had been instructed to "officially protest" Soviet failure to respond to repeated diplomatic requests for permission for Japanese search vessels to enter Soviet waters. Japan also announced it was joining the United States, South Korea and Canada in bringing the case before the United Nations Security Council.

The search for the plane's wreckage focused yesterday on an area 33 miles north-northeast of Moneron, where the Japanese patrol boat Chitose picked up a sample of oil from a 100-yard-long slick. Japanese officials said the oil was being brought to Japan for analysis.

Moneron is in the Sea of Japan, about 40 miles west of the southern tip of Sakhalin, and search ships were drawn to the Moneron area because it matched the plane's last location on military radar screens.

The search site also was consistent with a report from a Japanese fishing boat, the Chidori Maru, that seven crew members had heard two or three explosions and had seen flashes of orange light near Moneron at about 3:30 a.m. Thursday Tokyo time, and had then detected a strong smell of oil or gasoline. Secretary of State George P. Shultz said the plane disappeared from radar screens at 3:38 a.m. Tokyo time.

Japanese maritime officials said that Soviet planes and "six or eight" ships appeared to be searching the same area, with Japanese ships and U.S. planes scouring international waters nearby. The Japanese have sent 10 patrol ships to the area, while the United States has sent an AWACS surveillance plane, F15 fighter escorts and two air-sea rescue planes.

There was no hope of finding survivors in the 50-degree water, but search officials said the wreckage could help clear up the mystery of what had happened to the plane.

"The wreckage could be important proof," a Japanese Foreign Ministry official told The Associated Press before Abe's meeting with Pavlov. "A radar siting is not evidence, and that is one reason why we want to conduct a thorough search of the area."

But the Soviets "do not allow us to get into their sea territory, even for a humane reason," a Japanese Maritime Safety Agency official said.

New details of the plane's last hours continued to emerge. In Tokyo, Japan's national NHK network broadcast an account it said was based on 2 1/2 hours of Japanese military monitoring of Soviet radio transmissions. The network said three MiG23 fighters followed the airliner very closely, and the pilots' transmissions reportedly included the following, which could not be independently confirmed:

"Could confirm by eye."

"Had approached to two kilometers 1.2 miles ."

"They did not seem to notice us."

"Missile fire."

"Crushed down."

According to the network's account, broadcast Saturday morning Tokyo time, there was no sign the Soviet pilots tried to warn the airliner.

Before yesterday's Soviet statement was issued, a Soviet official, meeting privately with western correspondents in Moscow, offered another theory of what had happened to the plane. The unidentified official, the Los Angeles Times reported, suggested that the airliner might have been hit by cannon fire intended only as a warning.

Yesterday's Soviet statement offered no specifics to buttress its charge that the missing plane had been on an intelligence mission, but raised a series of questions about the manner in which the plane had been tracked by "the relevant U.S. services." Why, Moscow asked, did U.S. officials "not try to establish contact with the Soviet side and provide it with the necessary data about this flight?"

"In the light of these facts," the statement charged, "the intrusion into the Soviet air space by the mentioned plane cannot be regarded in any other way than a preplanned act. It was obviously thought possible to attain special intelligence aims without hindrance using civilian planes as a cover."

"Those who organized this provocation," the statement continued, "deliberately desired a further aggravation of the international situation, striving to smear the Soviet Union . . . "

Before the Soviet statement was issued, Korean Air Lines ordered an immediate change in the course of its Anchorage-to-Seoul flights. Airline officials said Flight 007 now would pass about 180 miles south of the Kamchatka Peninsula, rather than the 90 miles called for in the previous route. Both the Soviets and Shultz said the plane that vanished had crossed Kamchatka, one of the Soviets' most sensitive military areas.