Seven years ago this summer, strong public and private intervention by the United States probably saved the life of South Korean opposition leader Kim Dae Jung, who had been kidnaped in Japan by Korean CIA agents and taken bound and blindfolded onto a ship amid hints that he was to be heaved overboard.

As the crucial moment approached, Kim heard an airplane in the sky -- perhaps bearing a signal from authorities in Seoul -- and he said later that at that moment he sensed a sudden change in his captors' plans.

Today the controversial and colorful politician, who has been in and out of confinement several times in the interim, is facing the greatest danger since his experience on the kidnap boat in 1973. He is in prison awaiting court-martial on charges of sedition, which carry a maximum penalty of death.

According to veteran observers of the Seoul scene, Kim Dae Jung's life may once again depend on pressures and pleas from abroad, particularly from the United States.

South Korea's military leaders have thrown the book at him, charging him with violating five kinds of laws and regulations and strongly suggesting he was acting on behalf of North Korea.

The generals, to a notably greater degree than in the early 1970s, have passion in their voices when they speak of him. Some military men have told foreigners that it was a great misfortune that Kim was not killed in 1973, suggesting that is the fate they now may have in mind for him.

Since authorities made their charges against Kim known early this month, at least 10 nations including the United States have expressd their concern about his fate through diplomatic channels or public statements, and other nations are reported to be preparing to do so.

The United States said publicly through State Department spokesman David Passage that some of the charges "seem to be pretty far-fetched," while others "hardly amount to anything more than the charge that Kim Dae Jung was campaigning to be president."

Privately U.S. officials told Seoul that harsh treatment of Kim would have serious consequences in the United States, and Washington is known to have indicated that Kim would be granted political asylum in the United States if the Seoul government exiled him.

Foreign Ministry officials in Japan, which reacted angrily when Kim was kidnaped from there in 1973, have said the execution of the prominent opposition figure would revive the old controversy.

Diplomats in Canada, West Germany, Australia and New Zealand have expressed grave concern about Kim's future, and the Nordic countries of Sweden, Norway, Denmark and Iceland made a joint appeal to Seoul on Kim's behalf.

In an attempt to forestall a further buildup of international pressures, South Korean authorities last week publicly attacked "premature expressions of concern." The Foreign Ministry began calling in diplomats here to hear assurances that Kim's trial and treatment will be in keeping with law.

Foreign Minister Park Tong Jin in an interview said, "I am certain there will be a fair and open trial in this case."

He said that by "open," he meant the trial would be observed by the South Korean press and possibly by foreigners, but he conceded that large portions of the trial -- as in the recent case of the convicted assassin of president Park Chung Hee -- could be closed at the discretion of the judge on "national security" grounds.

Kim has not yet been formally indicted, although it is a foregone conclusion that he will be, and the trial is expected to begin before mid-August.

Korean officials are reported to be hopeful that the sensitive trial will be concluded before politically active universities reopen here late this summer.

Despite the fact that Kim received more 4 million votes -- about 45 percent of the total -- in his 1971 presidential race against the late president Park and has a substantial residue of political support, the opposition leader's friends said in recent days that domestic opinion is not likely to have much effect on the court-martial decision.

This is because the military seem to feel so strongly about Kim, and because he alientated a considerable part of his following by his ambitious maneuvering for the presidency following the assassination of his old opponent, Park.

The current allegations charge Kim with a long series of seditious actions, ranging from communist activity in his youth to plots against the government in the early and mid-1970s and finally to masterminding the riots and rebellion in the provincial capital of Kwangju this spring.

Unexplained in all this is why, if the charges are true, Kim was released from a previous prison sentence by Park in December 1978 and why he was released from house arrest in December 1979 and granted restoration of his civil and political rights this February by current President Choi Kyu Ha.

A senior general in the inner group of influential military officers insisted that "Kim was going to seize power" this spring, and maintained that "it was a real crisis for our survival."

Other Seoul observers said the generals feared Kim's political ability and public support could vault him into the presidency in the wake of the assassination of Park, with damaging effect on the position of the military leaders.

The consensus among independent observers is that considering the gravity of the charges, it is likely that if he is not executed, Kim will be sentenced to a long prison term spelling the end of his political career.