SEOUL, DEC. 11 -- Faced with a large bloc of undecided voters, the three main parties in South Korea's presidential campaign are engaged in a hectic scramble for last-minute support that has caused a marked rise in harsh rhetoric and political mudslinging in the final stage before next Wednesday's election.

Kim Dae Jung, one of South Korea's opposition presidential candidates, charged today that a 23-year-old Army corporal was beaten to death by his commanding officer after voting for Kim by absentee ballot. The allegation, if true, could seriously tarnish the government and ruling party.

President Chun Doo Hwan indirectly entered the fray by holding an emergency Cabinet meeting to discuss severe rioting that left 180 people injured at rallies yesterday for Roh Tae Woo, candidate of the ruling Democratic Justice Party.

A statement issued after the meeting described the violence as "a direct challenge to the authority of the government" and warned of "stern measures" if there is an outbreak of new rioting.

Ruling party officials accused opposition radicals of masterminding the attacks on Roh, but the opposition contended that police provoked the rioting.

The violence has heightened fears of either a military coup in the event of an opposition victory on Wednesday or explosive opposition protests if Roh wins.

A senior ruling party official, Hyun Hong Choo, said at a meeting with foreign journalists today that "there are genuine worries about whether an orderly election can be held" if there is continued violence.

"If we are unable to deal with the violence, it will mean a disruption of the election itself. It will be a disaster," he said.

Hyun, a top aide to Roh, raised the specter of angry mobs invading ballot-counting offices and burning ballot boxes if initial returns show the ruling party out in front.

Hyun also warned that what he called the ineptitude of opposition candidates Kim Young Sam and Kim Dae Jung would lead to anarchy within a few months should either of them take power in South Korea.

Such comments have helped create the tension here, but many political analysts and diplomats describe the warnings and rumors as tactics by the ruling party to scare voters into casting their ballots for Roh. A senior diplomat, playing down the coup rumors, argued that "the Korean generals are not like their counterparts in banana republics. Without justifiable reasons, {the Korean military} will not act."

While the focus of the ruling party is on political stability in the last days before the election, the opposition is charging that the government and ruling party are waging a corrupt election campaign.

Kim Dae Jung's charge about the death of the soldier, Chung Yun Kwan, is seen by observers as an attempt to underscore the opposition's contention that the ruling camp is using force as well as money to gain votes for Roh, who is viewed as being in a tight race with the two Kims.

If proven true, Kim's charge about the soldier's death could lead to an upsurge in antigovernment sentiment in the days before the election, many observers predict.

The soldier's father, Chung Myong Hwa, charged in an interview with United Press International today that his son was beaten to death on Dec. 4 by his commanding officer.

The father said military officials told him that his son was beaten for disciplinary reasons, not because of the way he voted, and that he later died of internal injuries. In the South Korean Army, beatings with fists and rifle butts are reportedly used to punish soldiers.

Kim Dae Jung said today that an investigating team from his party had determined that the commanding officer had tried to persuade six soldiers to switch their votes from Kim to Roh. When they refused, the officer began punching the soldiers, Kim said, and Chung Yun Kwan fell to the ground with fatal injuries. Another soldier allegedly was severely injured.

The National Defense Ministry denied Kim's allegations.

The ruling party's Hyun denied that commanding officers tried to influence the votes of their soldiers during the advance absentee balloting on military bases.

"These days, because of the political maturity of the overall population, no military leader can fool around with the idea of forcing and influencing his troops to vote for the ruling party," Hyun said.

The absentee voting by South Korea's 650,000 soldiers has emerged as a crucial issue. In past elections, intimidation of soldiers by commanders was reported to be widespread.

Citing security concerns, the military did not allow election officials on bases to observe the absentee voting, and there are fears -- and unsubstantiated reports -- that abuse may have been substantial. The margin of victory in the election could be narrow enough to be tipped by fraudulent military votes, some diplomats and experts said.