SEOUL, JUNE 24 -- Opposition politicians today denounced as a sham political concessions offered by President Chun Doo Hwan and suggested they would encourage an escalation of the two-week-old campaign in the streets against his government.

The statements dampened optimism that the two intensely hostile sides were close to a peaceful settlement of the protests. But government spokesmen played down the rejection as posturing and said the sides were still headed toward a "grand compromise."

Chun presented his concessions to Kim Young Sam, president of the main opposition party, in a three-hour meeting earlier today that included lunch. It was the first time they had ever met, an indication of the divisions in the political society here.

Chun offered to reopen negotiations in the National Assembly toward amending the constitution, effectively reversing an announcement he made April 13 suspending the talks until after the 1988 Summer Olympics in Seoul.

Reaching agreement on the revision is considered crucial to achieving long-term political stability in South Korea.

Chun said that Kim Dae Jung, who shares leadership of the opposition party with Kim Young Sam, would be freed from 2 1/2 months of house arrest. Busloads of police withdrew from his house late tonight, and supporters crowded into his garden to congratulate him.

Chun also told Kim Young Sam that the government would release as many as possible of the people who have been arrested since demonstrations began on June 10.

{The government said early Thursday it would release about 200 of 232 detainees, holding only those charged with murder, arson and other serious crimes, Reuter reported.}

{In Washington, President Reagan was briefed on the developments as the administration renewed a call for political dialogue and restraint. White House spokesman Marlin Fitzwater said the adminstration remains hopeful that the Chun-Kim discussions and other actions "will bring an end to the violence in Korea."

{State Department spokeswoman Phyllis Oakley called the meeting "an important initial step toward interparty dialogue and compromise."

{Gaston Sigur, assistant secretary of state for East Asian and Pacific affairs, ended a two-day visit to Seoul Thursday saying that his contacts with government, opposition, church and intellectual leaders left him confident that the dialogue between Chun and Kim would continue. Sigur responded to opposition statements that the meeting had failed by saying "You can't characterize one meeting as the end-all or be-all of everything," correspondent Lena Sun reported.

{Sigur said he had made it "crystal clear" to Chun that Washington opposed any military intervention in the crisis.}

Kim Young Sam told reporters that his side had won some minor victories but that in general Chun had failed to offer significant concessions.

"I reject the idea of resuming debate in the National Assembly. We wasted time for one year there," he said, referring to inconclusive discussions that ended with Chun's decision to suspend talks in April.

Kim said he told Chun that the question of what type of government to create should be put to a national referendum. "Let the people of Korea decide their fate," he said. But Chun did not agree to such a referendum.

Kim also assailed Chun for giving what he said were noncommittal answers on requests that 3,000 persons whom the opposition regards as political prisoners be released and to restore the political rights of Kim Dae Jung and others.

Before the suspension of talks in April, the opposition had proposed a referendum and is now calling it the most important issue. The government, however, has always said the problem should be settled in the assembly.

Today's events underscored the fact that reopening talks is only a small part of the task. Even before April, no substantial dialogue was going on, as the two sides had quickly become deadlocked.

The opposition wants a system headed by a popularly elected president. The government, however, is pressing for a cabinet system headed by a prime minister.

Kim Dae Jung, reached by telephone at his house tonight, said the government was retaining its plans to have Chun's chosen successor, Roh Tae Woo, elected under the current constitution late this year.

"President Chun is not ready to meet the people's urgent aspirations for democracy," Kim Dae Jung said. "There is no substantial change in Chun's attitude -- only lip service."

Kim Dae Jung also assailed Chun for suggesting that negotiations be conducted with Roh Tae Woo, suggesting this was a sign he was not sincere about change. "Roh Tae Woo is not the man who can decide such things," said Kim. "Only Chun can do it."

This afternoon, Chun went on to meet leaders of two minor opposition parties. He is to meet with church leaders Thursday, in what is being depicted as a round of consultations in all sectors of society aimed at helping him decide the best way out of the crisis.

Government spokesmen dismissed Kim Young Sam's remarks. "It's the beginning of a grand compromise," Choi Chang Yoon, vice minister of culture and information, said, referring to the meeting.

"He is impatient," Choi said. "Such impatience and rash reactions do not help anything." In politics, one should be happy with small victories, he said.

South Korean campuses were relatively quiet today, with the authorities reporting only 9,000 students taking part in protests at 45 campuses.

In Seoul, perhaps 1,000 students and labor union members fought running battles with police tonight near the Yongdong-po rail station in the city's southern sector. The clash grew from a rally that had been scheduled before Kim Young Sam's statement and did not seem to be a reaction to it.

Attention now is focusing on a "grand peace march" scheduled here for Friday evening. It is being organized by the same coalition that sponsored the June 10 demonstrations that began the current crisis.

Kim had said earlier that if the talks with the government went well, he would urge cancellation of that rally. He said today, however, that based on the government's proposals he could not urge cancellation.

A statement by his party tonight called the talks a "failure" and said that the party, "along with all other democratic forces, would fight to the end to achieve democracy and crush the government's plot to hold on to power permanently."

By offering negotiations, the government appears to be trying to break an alliance between students and middle-class moderates that has helped give momentum to the protests.

The turnout and response to the Friday rally will be watched closely here as a test of whether that strategy will work.

Sigur, who visited Chun and Roh this afternoon, drove to Kim Dae Jung's house tonight, where his car was briefly surrounded by people who chanted antigovernment slogans and rocked it menacingly. Several minutes later, the police cleared a path. Sigur spent about an hour talking with Kim.