SEOUL, NOV. 27 -- South Korean opposition leader Kim Young Sam has emerged as the front-runner in the perception of many people here as this nation prepares to hold a presidential election in 20 days.

With public opinion polls unreliable and their publication illegal, no one here can predict confidently the winner of South Korea's first democratic presidential race in 16 years. The four major candidates all hint at "December surprises" that could dramatically alter the standings.

But Kim, an opposition politician for almost three decades, has pulled off a series of public relations coups, establishing himself for now as the man to beat and pressuring ruling party candidate Roh Tae Woo into a highly negative campaign.

"The government here is not so confident of a victory," a western diplomat said today. "There is what Koreans call a wind for Kim Young Sam."

If elected, Kim, 59, would take over in what would be the first peaceful transition of powerin the republic's history. South Korea has been ruled by a series of strongmen who have tended to take over in military coups and then attempt to legitimize their position in carefully controlled elections.

Widespread street protests in June, however, pressured Roh and President Chun Doo Hwan to agree to opposition demands for a direct presidential election. In addition to Kim and Roh, fiery opposition leader Kim Dae Jung and former prime minster Kim Jong Pil are also hoping to be elected Dec. 16 and succeed Chun in February.

Chun has never been popular and Roh, his handpicked successor and a fellow general in the 1980 coup that brought Chun to power, has tried to distance himself from the president. Even a prominent Roh supporter said voters will pick the ruling party, not with enthusiasm, but because they fear instability if an opposition candidate wins.

"They'll say, 'I don't like this party, I don't like these people, but it's probably for the best,' " the Roh backer, a high-ranking official, said. He predicted a narrow Roh victory.

But several other observers said Kim Young Sam has persuaded some voters that he would be the best guarantor of stability. Few Koreans claim Kim is the brightest candidate or the best orator -- he recently embarrassed himself by appearing to confuse tactical nuclear weapons and nuclear power plants -- but he projects an air of comfortable middle-class solidity.

Bolstering that image, Kim recently attracted support from several retired generals and former top officials, giving his campaign an establishment air. Although Roh can claim experience in government, some voters and diplomats say they worry that a Roh win would prompt a renewal of protests.

Kim has bolstered his campaign further by recruiting a few former supporters of Kim Dae Jung and enough antigovernment activists to confirm his credentials as a fighter for democracy. Kim Dae Jung's supporters appear the most ardent of any candidate's, but some observers question whether his campaign aimed explicitly at South Korea's "have-nots" can win a plurality of voters in an increasingly middle-class country.

Both Kim Dae Jung and Kim Jong Pil are having trouble raising money and have published newspaper ads soliciting contributions. Both claim government pressure on corporate givers has hurt them.

The picture could change many times between now and Dec. 16. Kim Dae Jung, in particular, is a savvy politician who has been distracted until recently by battles within the opposition.

"I expect him to start moving soon," a ruling party official said. Kim Dae Jung's supporters are hoping that a big rally planned in Seoul on Sunday will give him a boost.

Kim Young Sam, meanwhile, has "a terribly disconcerting habit of putting his foot in his mouth," a diplomat said. Many observers predict he would fare poorly in television debates, which are tentatively scheduled for next month.

But Kim Young Sam's success so far has apparently forced the ruling party to change its strategy. Roh at first portrayed himself as "a common man" who would take the high road and not make many promises.

Recently, however, Roh has attacked Kim Young Sam and warned that an opposition win would end South Korea's prosperity, plunge the nation into chaos and ruin the prospects for the Seoul Olympics, scheduled for next September.

The ruling party candidate also has criss-crossed the nation promising airports, electric rail lines, industrial parks and dozens of other development goodies. In addition, the government has been taking a hard line against activists working for any of the "three Kims." This week, police said they might arrest 21 college professors for issuing a statement urging Roh to withdraw.

All three opposition candidates also claim the government has escalated its use of dirty tricks. Kim Jong Pil charged Wednesday that normally scheduled promotions of military officers have been delayed until after the election so that the officers can be evalulated on how well they deliver votes from their Army units.Special correspondent Peter Maass in Seoul contributed to this report.