SEOUL, JULY 19 -- Soh Joon Shik's term in a South Korean jail was supposed to end in 1978.

Because Soh will not admit that he spied for North Korea, however, and because he will not repent and convert to "anticommunism," he remains in jail, his term extended two years at a time by order of the justice minister.

Soh is one of scores and perhaps hundreds of political prisoners left behind after a government amnesty freed hundreds during the past two weeks. Those still in jail illustrate the troubling division within South Korean society as this nation attempts to move toward democracy, and their continuing imprisonment may deepen those fissures.

To the opposition here, to some western diplomats and to Amnesty International, many of those still behind bars are prisoners of conscience: students, labor leaders and others whose only crime was to fight for democracy. Many have been tortured, according to credible reports, and after years of living under stark prison conditions many are in poor health.

To the government, the remaining prisoners are spies or communists who would menace society if freed.

The prisoners themselves cannot speak directly, but their presence is sharply felt on the political scene -- through a moment of conversation stolen in a jailhouse corridor and later reported by a freed companion, or a photograph of an alleged torture victim displayed at a rally, or the unflagging testimony of relatives.

"It's going to be a very emotional issue," one western diplomat said. "The families of the prisoners form such a hard-line constituency, they're willing to take to the streets, and they can drag the mainline dissident community along with them."

Min Hyang Sook, 36, is not actually a relative. She was 25 days away from marrying her fiance when he was taken away in 1975. Since then she has had no direct contact with Lee Chul; once each month they can shout to each other through a thick glass window while prison guards take notes.

Min said that her fiance, an ethnic Korean who grew up in Japan and came here to study, was accused of traveling to North Korea, spying for that communist nation and distributing pamphlets critical of South Korea.

According to Amnesty International, Lee was held incommunicado for 40 days and then confessed. He later withdrew his confession, saying he had been tortured and told that his fiancee and family would be tortured, too.

An investigation by the Tokyo Bar Association concluded that Lee had credible alibis and was innocent, no more than a political opponent of the South Korean regime. But he received a death sentence, later commuted to 20 years in prison.

"He was a kind of political scapegoat to maintain {then-president} Park Chung Hee's power," Min said.

An official of the Catholic Peace and Justice Committee agreed. "Whenever they are in some critical situation or crisis, they 'uncover' a spy ring," the official said.

The official also said that many Japanese Koreans, including Lee and Soh Joon Shik, have been jailed or come under suspicion here because they grew up in a freer society in Japan, where reading and discussing Marxism was permitted. Many of them reach Seoul unprepared for the limits on political speech that prevail here, she said.

During Lee's first 3 1/2 years in prison, his handcuffs were never removed, even for meals, Min said. In 1985, he joined with 18 other prisoners to petition for better treatment.

Guards in the Taegu jail responded by taking the 19 to a basement room, binding them and kicking them repeatedly, Min said.

"He fainted, and when I visited the prison he had to be carried out by five people," she said. "He couldn't open his eyes."

During the past two weeks, the government has released more than 400 political prisoners and restored civil rights to more than 2,300 former prisoners. The releases, mostly of short-term inmates, were part of an amnesty promised by President Chun Doo Hwan, along with free elections in the fall, after large-scale demonstrations in June threatened to topple his government.

Officials say that fewer than 100 political prisoners now remain in jail, while opposition figures say the number is in the hundreds. No one knows exactly how many there are, nor how many convictions might have been based on real evidence -- how many are spies or violent revolutionaries, and how many are simply opponents of South Korea's authoritarian regime.

Among those still in jail are key antigovernment leaders of the past few years, such as Kim Keun Tae, and longtime prisoners who were jailed for opposing the Park government in the 1970s.

"There were so many faked criminal records, including {opposition leader} Kim Dae Jung's, that where is the limit?" asked Hong Seung Chik, a sociology professor at Korea University. "We just don't know."

The issue is clouded because the government, citing a constant threat from the north, views as dangerous those who support any degree of communism, and even opposition leaders Kim Dae Jung and Kim Young Sam have said that communists should not be released from jail.

"Unlike other countries where the Communist Party can function, communism here is not regarded as a simple ideology," explained Shin Hyun Gook, a government spokesman. "We think communism is totally antistate and denies our own existence. . . . Any act implying communist thinking would be regarded as a criminal act."

In addition, the government appears divided over the wisdom of the past weeks' releases. Some officials in the vast security bureaucracies, including many prosecutors who helped put dissidents behind bars, object to these prisoners' freedom, whether they are communist or not.

Activist leaders believe the government may be holding some prisoners to use as bargaining chips in coming negotiations with the opposition about a new constitution and fall elections. The government may also fear a loss of credibility if it releases prisoners it had described as dangerous.

Some prisoners' relatives believe that high-ranking police officials are fighting releases to protect themselves.

"They tortured many people, they executed some, and now they don't want all these people who have been wronged coming around and accusing them," said So Hae Pyon, whose husband has been in jail since 1979.

So is a leader of the prisoner family movement, and in her determination can be seen the potential explosiveness of the issue. She speaks matter-of-factly about alleged mistreatments such as the hot pepper torture, in which fiery water was poured into prisoners' noses and down their throats; about the chicken-roasting torture, in which prisoners were trussed to a pole and spun; about sexual abuse of female prisoners; about the no-sleep torture and the water torture, the kind that the government has admitted led to a student's death in January as his head was repeatedly thrust into a tub of water.

The government has denied that torture of prisoners is widespread, but did admit that the student died under torture while in confinement. Police involved have been sentenced to jail.

So and her compatriots want their relatives out. In many cases, they also want alleged torturers brought to justice. The very sight of the long-term prisoners, if released, could inflame feelings further.

"They are in bad condition," the official from the Catholic committee said. "Because of the malnutrition, their teeth are rotting, their hair has turned gray, their stomachs are bad, they have bad arthritis."

"Prison conditions in Korea are very stark," a western diplomat agreed. "Prisoners, whether thugs or students, are in for a very, very rough time."

The government says it will not be pressured into unwise releases. No more are planned, officials said this week, although circumstances could change.

Rep. Thomas Foglietta (D-Pa.), who talked with ruling party officials during a recent visit here, said the question remains open.

"There will be more releases, but I think they're going to be screened very, very carefully," he said.

Caught in the middle are opposition politicians, calling for releases in the name of national reconciliation without proclaiming the innocence of all those who remain in jail.

Prof. Hong, who heads the Asiatic Research Center, said the fate of the prisoners will be seen by many as a test of "government sincerity" about democratization. He said the nation's ability to tolerate dissidents, even radical ones, will pose a more fundamental test.

"I think we should learn how to live with discontented people," he said. "I think we have to learn how to live with them, rather than trying to eliminate them."