SEOUL, JUNE 26 (FRIDAY) -- Tens of thousands of South Korean police mobilized today to break up mass rallies that dissidents plan to stage in Seoul and other cities this evening to resume street pressure on the government, despite President Chun Doo Hwan's political concessions.

The police statement came as the government said opposition members should seek to settle a two week-old political crisis through dialogue and "end their insistence on solving all problems hastily in one sweep."

With organizers refusing to call off the rally, the stage seemed to be set for explosive clashes. The cities have been comparatively quiet in recent days while the government and opposition negotiated.

Emotions were likely to be raised by news of the death Wednesday night of a protester who was injured last week during a protest in Pusan city. He is the first demonstrator to die since the street actions began June 10. One policeman has been killed.

The authorities placed dissident leader Kim Dae Jung back under house arrest, only one day after having released him as one of Chun's concessions, a spokesman for Kim said.He added that local authorities told Kim today that he should not leave his house in western Seoul. Other people have been free to enter and leave the compound, which is surrounded by about 400 riot police.

Hopes for meaningful negotiation between the government and opposition were set back for the time being Wednesday after a meeting between President Chun and Kim Young Sam, head of the main opposition party. Kim told reporters that concessions Chun offered during a three-hour session with him were not meaningful and that he could not advise people to stop demonstrating.

A National Police statement yesterday declared tonight's rallies illegal and said that to suppress them, police will question people on the streets, block traffic, seize demonstration equipment and arrest people disobeying orders to disperse.

Many student and dissident groups have said they will turn out in force for the rally.

Analysts here will be watching the numbers and determination of the demonstrators as a measure of whether the opposition's campaign, the greatest threat ever mounted to Chun's seven-year-old rule, has run out of steam.

The rally is being organized by a group called the National Coalition for a Democratic Constitution. It brings together activist clergymen, dissident politicians, students and other opponents of the government.

The group said the rally will be nonviolent. But the police reject the claim.

"The reckless and illegal demonstrations planned by the National Coalition for June 26 are aimed at driving society into extreme chaos and anxiety to achieve its subversive political objective," the police statement said.

The police will "resolutely deal" with the rally, it said. But with authorities hesitant to impose emergency steps, it was unclear how successful the police will be in blocking it. Their normal tactics of tear gas and mass formation sweeps have had only limited effect in controlling large turnouts in the past two weeks.

Meanwhile, President Chun met yesterday with Cardinal Kim Sou Hwan, leader of South Korea's 2 million Catholics. Kim reportedly urged Chun to amend the constitution to provide for direct election of the president, which is what the opposition wants. He also raised the possibility of putting the question of governmental system to a national referendum.

Presidential spokesman Lee Jong Ryool said yesterday Chun's consultations with Cardinal Kim and opposition party leaders mark "the beginning of a quest for a grand compromise." "Both the government and the opposition should make progressive and constructive efforts to work out a formula to resolve the current situation," Lee said.

"The political opposition should end their insistence on solving all problems in one sweep and should instead approach the issue in a more patient and earnest attitude," he added.

Dissident leader Kim Dae Jung stayed home yesterday, meeting supporters, journalists and Kim Young Sam.

Korean newspapers reported that on Monday the government will release about 200 people arrested since the current demonstrations began and who still are in jail. That was one of the concessions offered by Chun to Kim Young Sam Wednesday.

About 120 other people will remain in detention for now, at least, pending investigation of charges against them, newspapers reported.