SEOUL, OCT. 10 -- South Korean opposition leader Kim Young Sam, deepening the split in South Korea's antigovernment coalition, officially declared his candidacy for president today in the country's upcoming election.

At a hastily arranged press conference, Kim, president of the opposition Reunification Democratic Party, lashed out at the government and ruling party, accusing them of "trying to prolong the military dictatorship against the people's will." He added that he aims to "accomplish a democratic revolution through peaceful means."

Kim's announcement was widely expected. He has said informally on several occasions in the past two weeks that he planned to run. But the declaration is certain to sharpen the divisions between Kim Young Sam and his opposition rival, Kim Dae Jung, who has strongly hinted that he, too, plans to run in the elections, which are to be held before Dec. 20.

The two Kims had set a Sept. 30 deadline for deciding which one of them would be the opposition candidate. But the intense negotiations between the longtime rivals broke down during a head-to-head meeting 10 days ago. At the bargaining session, each of the Kims demanded that the other step aside, and each refused to do so.

Kim Young Sam's declaration today, apparently timed to upstage an expected declaration by Kim Dae Jung next week, thus marks another stage in the intense political jockeying between the two opposition leaders.

Kim Young Sam said he would continue to seek dialogue with Kim Dae Jung in order to reach a decision on a unified opposition slate. But a senior aide to Kim Young Sam said the opposition party president has no intention of withdrawing his candidacy.