South Korean opposition leaders said they would continue and expand their efforts to change the country's constitution one day after President Chun Doo Hwan met with opposition members Monday in an attempt to defuse the rising political tension surrounding their petition drive.

Opposition sources in Washington said the timing of the meeting appeared to be influenced by the international scrutiny and coverage of the political unrest in the Philippines and a desire on the part of the government in Seoul to avoid drawing similar attention, particularly from Washington, to events in another country closely allied with the United States.

The opposition, contending that the present electoral college system gives the incumbent an unfair advantage, wants to amend the constitution to allow selection of a president by popular vote when Chun's term expires in 1988.

The Chun government has maintained that, in the interest of a peaceful transition, any debate on changing the constitution can only happen after 1988, and that the petition drive mounted by the opposition is illegal.

Since the campaign began about two weeks ago, the government has arrested scores of opposition figures and prevented them from entering their party headquarters.

Chun met Monday with members of the two main opposition parties.

There are varying accounts of what was said, according to sources who follow the situation closely.

But from all accounts, the meeting was significant because Chun appeared to be moving away from confrontation and toward the beginning of a dialogue with the opposition, the sources said.

According to opposition sources in Washington, Chun said he would not use police force again to prevent opposition members from entering their party headquarters.

According to Korean officials and opposition sources, Chun, in a departure from government policy, also agreed to form a committee to review the constitution with the explicit aim of amending it.

Opposition sources said there was no substantive change, however, because Chun said such changes could not take place until after 1988.

When he was asked by Lee Min Woo, president of the main opposition party, the New Korea Democratic Party, whether the petition drive was illegal, Chun avoided an answer and took a vague position, opposition sources said.

Yesterday, Kim Dae Jung and Kim Young Sam, who share de facto leadership of the New Korea Democratic Party, said the government's position was "incomprehensible" and not worthy of "serious discussion," according to an Associated Press report from Seoul.

In a joint statement, they said, "We are all watching the Philippines because there are striking similarities to South Korea."

They said the Philippines demonstrated a "domino trend of democracy" that could affect Asia and other parts of the world.

If the situation in South Korea were allowed to worsen, they said, it "could develop into another Philippines situation."