Kim Dae Jung's involvement seven years ago in an episode of South Korea's turbulent exile politics is at the core of a charge that could cost the former political leader his life.

The episode has been forgotten by most South Koreans and remained a dusty footnote in history until it was revived by military prosecutors for the current trial in which Kim, if found guilty, may face the death penalty.

The government is charging that Kim helped to found an organization called Hanmintong in 1973 in Japan and that many of his associates in its formation were people sympathetic to enemies, the North Korean Communists.

So unfamiliar is the case to South Koreans that the government-owned television station was instructed to prepare a two-hour program explaining what it was all about. The show refers to Kim's role in Hanmintong and asserts that money for its founding came from North Korea. The production was shown in prime time this week, as the trial was under way, in an apparent attempt to build a public opinion hostile to Kim.

Most of the attention in the trial has focused on allegations that Kim encouraged student demonstrations and a insurrection in May as an attempt to create chaos from which he would emerge in power. He has denied any such plot.

However, government officials explained this week that Kim's life does not hang on the charge of plotting sedition that has received so much attention. Instead, they said, the death penalty could be imposed because Kim helped to found Hanmintong, the antistate organization that most people had thought extinct.

Its origin lies in the ferocious antipathies of Korean exile groups. Many South Koreans living abroad, in Japan and the United States, were hostile to the government of the late president, Park Chung Hee. After losing narrowly to Park in the 1971 presidential election, Kim went abroad and sought to organize South Koreans emigre groups in Tokyo and Washington into an anti-Park foreign lobby that could influence foreign governments.

His major activities were in Tokyo, which is home to two rival Korean organizations, one that supports South Korea and one that favors the communist government in Pyongyang. Kim has acknowledged joining in preparations for the Hanmintong organization in August 1973, but he was not present for its actual formation. The reason is that he had been kidnaped from a Tokyo hotel room, reportedly by South Korean government agents, and forcibly returned to Seoul.

Now, seven years later, the government indictment charges that Kim was linked in the preparations for Hanmintong with several other South Koreans who had been expelled from the pro-South Korea organization and worked closely with the pro-North Korea group. Kim has denied knowing that they were supporters of the communist government.

The manner in which the old connection has been revived to make a criminal indictment seems tortuous to some observers of the trial.

Government officials were asked why, if the Hanmintong connection is such a crime, Kim was never charged with it before. One responded that the government had just begun to "focus" anew on Kim's past when he began agitating against the government last spring.

Another, however, acknowledged that the real reason was the government's fear of anger from Japan. Kim's kidnaping had created a storm of controversy that still prevails in Tokyo where the government has been under continuous pressure to assert an interest in Kim's welfare. The Japanese govertnment has agreed not to seek penalties for the violation of sovereignty involved in his kidnaping so long as Kim was not prosecuted for his activities in Japan.

The government charges that Kim kept in contact with Hanmintong agents after his forced return to South Korea, but the indictment mentions only four incidents in which he either talked by telephone or sent messages through third parties.

None of them involved any organizational matters except for Kim's request to be removed as chairman, a position to which he had been elected in absentia.

The trial of Kim and 23 others accused of antigovernment activities was recessed today until Tuesday, in part to give court-appointed defense attorneys time to examine documents.