The Soviet Union moved today to bolster its case that it acted properly in shooting down a South Korean airliner by inviting western journalists to question the head of its armed forces, Marshal Nikolai Ogarkov.

In Tokyo, the Soviet ambassador told Japanese Foreign Ministry officials that his government would soon deliver debris and "documents" found in the search for the downed plane. Story, Page A8.

The announcement of the press conference Friday with Ogarkov, who will be accompanied by senior Communist Party and Foreign Ministry officials, coincided with a major propaganda counteroffensive by the Kremlin following the storm of criticism in the West over the destruction of the airliner with the loss of 269 lives.

After belatedly acknowledging that the Korean Air Lines plane was shot down by a Soviet fighter, Moscow has sought to shift responsibility to the United States with allegations that the plane, a Boeing 747, was engaged in an intelligence mission.

The decision to allow Ogarkov to be questioned by western journalists was seen here as a measure of the Kremlin's concern over the airliner disaster's effect on the Soviet Union's international image at a time when it is trying to win support for its policies on arms control.

As chief of the general staff of the Soviet armed forces, Ogarkov theoretically was responsible for the order to shoot down the plane, even though Soviet officials have suggested privately that the decision was made at a lower level.

Foreign observers in Moscow could not recall a precedent for such questioning of a military figure of Ogarkov's standing during a major international crisis. Although President Yuri Andropov has brought a slightly more open style to government, the Soviets remain almost obsessively secretive about security issues.

Among the other Soviet officials who will take part in the press conference are Leonid Zamyatin, head of the Communist Party's International Information Department, and Georgi Kornienko, first deputy minister of foreign affairs. A press conference scheduled earlier with a deputy minister of civil aviation was canceled.

Soviet officials hinted privately that the Kremlin may use the press conference to release evidence supporting its contention that the South Korean pilot ignored warnings that his aircraft had intruded into Soviet airsparce.

A major element in Moscow's defense is expected to be its claim that the Soviet pilot who shot down the plane had tried to make contact with the airliner on the international emergency radio frequency of 121.5 megacycles. A source at the official Soviet information agency Novosti said today that the pilot had activated equipment that automatically emits internationally recognized signals on this frequency, warning the South Korean pilot that he was over Soviet territory. The pilot received no response, the source said.

President Reagan has said that Soviet fighter planes are not fitted with such radio equipment for fear that it could be helpful to pilots wishing to defect. U.S. officials insist that the South Korean plane was shot down without warning.

A U.S. Embassy spokesman said the Soviet Foreign Ministry has not responded to repeated requests for more information about the jetliner's crash or for permission to search for wreckage in Soviet waters.