SEOUL -- With South Koreans scheduled to elect a new president in less than eight weeks, four leading contenders have embarked on a course of political brinksmanship that has left many voters anxious about the durability of their fledgling democracy and concerned about instability even after the vote.

A full-fledged election campaign is under way here now, something that was hardly conceivable even six months ago in a country that has been ruled by military-installed governments for years.

Yet the manner in which it is unfolding is unsettling many voters. There is bitterness and frustration over the splintering of forces opposing the ruling party candidate and concern that a minority government might emerge that would have trouble leading this increasingly powerful nation.

The country is expected to overwhelmingly approve a new constitution in a referendum next week, setting the stage for South Korea's first contested election in 16 years. The political gossip in Seoul's coffee houses and ward offices has become reassuringly mundane; where tear gas and molotov cocktails set the tone only four months ago, the talk now is of the woman's vote and television debates.

But the fracturing of both the conservative side and the opposition, which has produced four major candidates in the process, has become a problem rather than a celebration of newly found democracy.

"I worry, because more and more people are feeling disgusted," said Lee Shin Bom, a former student leader now active in opposition politics.

Earlier this week, a group of junior lawmakers of the opposition Reunification Democratic Party proposed that the party vote to produce a single candidate if the two leading opposition figures, Kim Young Sam and Kim Dae Jung, cannot agree on which one of them will stay in the race.

Under pressure from wide-scale street protests in June, President Chun Doo Hwan promised on July 1 to allow direct elections in December and step down next February, permitting the first peaceful transition of power in this nation's history. South Koreans hailed his concession as opening a new era in a republic that has been governed by military or civilian strongmen since its birth.

At the same time, Chun agreed to restore the political rights of longtime opposition leader Kim Dae Jung. Cynical observers said then that Chun was freeing Kim to make war on rival opposition leader Kim Young Sam, thereby splitting the opposition and giving the ruling party its only hope of winning a free election.

The two Kims promised repeatedly that such a split would not occur, that Kim Young Sam, the establishment oppositionist, and Kim Dae Jung, the charismatic outsider, would unite. But those promises are withering in the heat of long-suppressed ambition, intense regional rivalries that play perhaps the leading role in determining whom people will vote for, and personal animosity.

"They are like two armies," said Lee Shin Bom, referring to the two Kims. Lee and many others feel that at the last minute, one may withdraw. "But they can't quit now. If they do, they lose everything, their supporters and their money."

Kim Young Sam, puffed with success after a huge political rally in Pusan last Saturday, said in an interview that he has no choice but to run. Neutral observers estimated the crowd between a half-million and 1 million, while Kim said more than 2 million attended. "It was the largest political rally ever held in the world," Kim said this week.

Kim, whose home base of Pusan and southeast Korea long has dominated the nation's politics, increasingly dismissed Kim Dae Jung's contributions to democratization during the past 20 years.

"I have never departed from the people who have been struggling and suffering under dictatorship," Kim said, taking an indirect shot at Kim Dae Jung, who went into exile after Chun sentenced him to death in 1981.

Kim Dae Jung has been more restrained in his comments about his rival, saying both contributed to democracy, although "the people who took to the streets" truly brought democracy.

But Kim Dae Jung, too, said he must run. Workers, students and his neglected home region of southwest Korea would not forgive him otherwise, he said.

"If I did not run, my supporters would probably start riots against that decision," he said. "I could never return to my home province because I would be labeled a traitor to my home . . . I am in a dilemma."

Kim said he believes both opposition leaders should run and, one week before the election, the weaker should bow out if the ruling party appears headed for victory.

A western diplomat said that Kim Dae Jung is "still the best politician of the four -- the best informed, the best speaker, the quickest, the best political mind." But Kim is also the most controversial, anathema to some military officers and under attack for breaking a promise last November that he would not run.

At the same time, some believe Kim Dae Jung may once again see himself as a martyr and, at the last minute, sacrifice his campaign in the name of having a single opposition candidate to defeat ruling party candidate Roh Tae Woo.

". . . His final martyrdom, his final gift to his country," could be "not to run," one diplomat said.

Ruling party candidate Roh, native to the dominant southeast, would seem poised to profit from the two Kims' split. With the bureaucracy, a friendly press and the most sophisticated campaign operation on his side, Roh has moved his image beyond that of a former general and Chun crony, calling himself a "common man" who can bring democracy with stability.

Publication of opinion polls is illegal in South Korea, but many are being conducted, including by the ruling party. A political insider with access to some polls said that Roh probably would lose a two-way race, but that with both Kims running, his chances of winning are good.

Regional rivalries would then cancel each other out, the insider said, giving Seoul a deciding vote. Half of this fast-growing capital's 10 million residents consider themselves middle class, with a stake in stability and continued economic growth, he added.

"Seoul is the key, Seoul will decide," he said. "And right now Roh is way ahead in Seoul."

But Roh's campaign tour through Kim Dae Jung's home province this week showed weaknesses in popularity and campaign organization. Roh was greeted with small and sullen crowds, pelted with eggs, met by demonstrators and interrupted by tear gas.

Kim Jong Pil, prime minister under an earlier regime, is Roh's other problem. Many voters dismiss "the third Kim" as a remnant of a discredited dictatorship, but some say that Roh's political inexperience and the opposition's squabbling make "JP" an attractive alternative.

Kim Jong Pil is likely to take votes from the ruling party, and many establishment figures have urged him to drop out. If the opposition unites, such pressure on Kim Jong Pil would increase.

But the former premier was vilified and humiliated by Chun and Roh and their comrades after their 1980 coup, and he has waited quietly for a chance to set the record straight.

Thus, a new president could be elected with less than 30 percent of the vote, leaving him without a mandate. Kim Dae Jung could face trouble from a suspicious military, Roh Tae Woo from students and the political left.