SEOUL, JUNE 27 -- The ruling Democratic Justice Party today hinted at new concessions to the opposition, as Seoul and about 30 other cities cleaned up after large antigovernment demonstrations yesterday.

Students numbering in the hundreds staged hit-and-run protests in at least two areas of Seoul. But in general the capital and provincial cities rocked by often-violent rallies yesterday were quiet today.

One of the broadest suggestions of new flexibility in the government came from Lee Choon Koo, secretary general of the ruling party.

He was quoted today as saying it was "unthinkable" that the current constitution would remain in force long enough for President Chun Doo Hwan to use it to transfer power to a successor next February.

His remarks came with other press reports and statements by ruling party officials suggesting willingness to discuss immediate constitutional changes, as well as cancellation of the June 10 nomination of Chun's chosen successor, Roh Tae Woo.

Under another proposal that was discussed at a ruling party caucus today, a new general election would be called after dissolution of the National Assembly.

There was no firm commitment to do any of these things, however. It was also unclear how the opposition would react to them.

Kim Young Sam, president of the main opposition party, talked with Chun in an unprecedented three-hour meeting Wednesday. Kim later called the meeting a failure, saying Chun had agreed only to discuss constitutional change, not to grant opposition demands about how and when to implement change.

At the meeting, Kim also spurned Chun's suggestion that he meet with Roh and continue negotiating a settlement to a crisis of street demonstrations that erupted 2 1/2 weeks ago.

An estimated 500 students staged protest gatherings this afternoon near Seoul's East Gate, drawing police tear gas. Several hundred others fought police in the vicinity of Seoul's main rail station.

In Kwangju city, police fired tear gas and about 2,000 students threw rocks tonight along a main avenue of the city. At one point, students atop three office buildings dropped fire bombs toward police below.

The semiofficial Yonhap News Agency reported minor protests in a half dozen other cities.

Police said they had released all but about 800 of more than 3,460 people arrested nationwide during yesterday's protests. Official statistics put the tally of damage at nine vehicles burned and 39 police stations and posts attacked.

More than 570 policemen were said to have been injured. As is usual, the authorities offered no numbers for demonstrators injured.

Meanwhile, prosecutors asked for sentences of up to 15 years for five policemen charged in the death of a student activist during torture in January.

Public outrage over the death is commonly believed to be one reason why antigovernment demonstrations have continued with such force.

When the sentencing requests were announced, a group of about 100 people, including the student's parents, went on a brief rampage in the courtroom, shouting that the sentences were "too light for murderers." They broke chairs and threw eggs in the courtroom, according to witnesses.

Washington Post staff writer Stuart Auerbach reported the following in Washington:

The Senate yesterday added its voice to Reagan administration pressure on the government of South Korea to renew negotiations with the opposition to get a peaceful transition to full democracy.

The nonbinding resolution was unanimously approved, 74-0, during a rare Saturday session to take up a 1,000-page trade bill. It's main sponsor, Sen. Dennis DeConcini (D-Ariz.), said it would likely keep the Senate from adopting a more restrictive amendment being proposed by Sens. Edward M. Kennedy (D-Mass.) and Barbara A. Mikulski (D-Md.). This would take special trade preferences away from Korea if it fails to make a peaceful transition from military rule to a freely elected government.