About 50,000 persons rallied peacefully here today against the government of President Chun Doo Hwan, as the South Korean opposition movement pressed a campaign to bring down what it calls a military dictatorship.

It appeared to be the largest opposition demonstration in South Korea since a violent insurrection against Chun in this southern city was put down forcibly in 1980.

After the rally broke up, several hundred people, most of them students, skirmished with riot police tonight. Things returned to normal at midnight after 69 of these protesters were arrested in a group in a city plaza.

But in general, the Easter Sunday gathering, held in a downtown area where much of the killing in 1980 took place, was marked by discipline, high spirits and occasionally emotional expression of grief for the dead.

"To achieve democracy is the only way to soothe the souls of the victims of the Kwangju incident," Kim Young Sam, a senior opposition leader, told the crowd in a speech.

Another senior dissident leader, Kim Dae Jung, did not attend, because police blocked him this morning from leaving Seoul, the capital. Kim's car was stopped by police vehicles as it was taking him to the airport to board a flight for Kwangju.

In a recorded speech played to the crowd, Kim said that South Korea and the Philippines, where president Ferdinand Marcos' 20-year rule was ended last month by a popular and military revolt, have differences but also important similarities. "In both, dictatorship has been up against the people's desire," he said.

The rally marked the local kickoff of a national petition campaign calling for the direct election of the president in South Korea. The campaign is the centerpiece of the fight against Chun, who the opposition says could not survive a fair election.

The significance of the rally was not so much its size -- Kwangju traditionally has been firmly in the opposition camp -- but the fact that the government allowed it to take place. Until last month Chun was trying to stamp out the signature campaign, but, apparently having decided that that approach was not working and causing bad publicity, he has eased up and is letting it proceed.

The day's events began at 2 p.m., when several hundred members of the opposition New Korea Democratic Party convened a meeting in a muggy gymnasium in the local YMCA. Speeches were piped by loudspeaker to the crowd outside.

For six years, memories of the Kwangju revolt have sullied Chun's attempts to establish legitimacy at home and abroad. To his critics, the former Army general is a man who had blood on his hands when he formally assumed the office of president in the summer of 1980.

The revolt was sparked on May 18, 1980, when Chun and his group of generals began a crackdown on opponents and arrested Kim Dae Jung, who is a native of Kwangju Province.

Demonstrations in the city escalated and, as the government used force in vain efforts to put them down quickly, became a full-scale insurrection, with rebels taking control of government buildings and weapons. In the end, the Army crushed the revolt with gunfire.

The official government statistics show that 201 persons were killed, including some soldiers and police, but many people here say the figure was much higher.

Chun's government maintains that the suppression was tragic but unavoidable, due to a need to maintain unity against a military threat from Communist North Korea and that people should put the Kwangju incident behind them.

But many people in this city refuse to forget. "We made many sacrifices in 1980," said K.W. Son, a student who signed the petition this afternoon as the rally was going on. "We must continue to oppose dictatorship."

For years, many people in Kwangju have been demanding a full investigation and punishment of those responsible, who in their eyes is primarily Chun. Much of what anti-American sentiment exists in South Korea grows from the belief that the United States cooperated with Chun in Kwangju. U.S. officials in Seoul deny any role.

Today's crowd reflected a cross section of the city's 1 million inhabitants, with blue- and white-collar workers, elderly men and a few children. Many people wore yellow ribbons on their lapels, signifying that they had signed the petition.

They listened to speeches for close to four hours, after which Kim Young Sam and Lee Min Woo, president of the opposition party, and others led a march along busy city streets for a half mile to the local party's headquarters. The crowd chanted, "Down with dictatorship!" and the names of the two Kims.

After Kim and Lee left, militant students in the marchers' ranks returned to the plaza and began a running battle with hundreds of helmeted riot police, throwing rocks and bottles. Police used tear gas.

Student-police clashes are an almost daily occurrence in South Korea. However, mass arrests of this kind are relatively rare. eyes is primarily Chun. Much of what anti-American sentiment exists in South Korea grows from the belief that the United States cooperated with Chun in Kwangju. U.S. officials in Seoul deny any role.

Today's crowd reflected a cross section of the city's 1 million inhabitants, with blue- and white-collar workers, elderly men and a few children. Many people wore yellow ribbons on their lapels, signifying that they had signed the petition.

They listened to speeches for close to four hours, after which Kim Young Sam and Lee Min Woo, president of the opposition party, and others led a march along busy city streets for a half mile to the local party's headquarters. The crowd chanted, "Down with dictatorship!" and the names of the two Kims.

After Kim and Lee left, militant students in the marchers' ranks returned to the plaza and began a running battle with hundreds of helmeted riot police, throwing rocks and bottles. Police used tear gas.

Student-police clashes are an almost daily occurrence in South Korea. However, mass arrests of this kind are relatively rare.