SEOUL, JUNE 19 (FRIDAY) -- State-run radio said this morning the South Korean government has concluded that "emergency measures" are "inevitable" if violent street protests here continue to worsen. The statement followed rioting by tens of thousands of people last night that turned the centers of Seoul and other major cities into virtual war zones.

The warning coincided with government efforts to arrange a peaceful solution to the crisis through concessions to the opposition. The radio did not specify what the emergency measures might be or whether they would affect the attempts at conciliation.

The state-run Korean Broadcasting Service said that Prime Minister Lee Han Ki will issue a formal statement soon concerning stern measures unless things calm down. A decision to make that warning was reached at a meeting this morning of security-related Cabinet members, it said.

At one point yesterday, the protesters overran a unit of about 80 policemen, beat some of them badly and burned their shields, masks and tear gas rifles in giant bonfires. They attacked at least one police station and burned a police bus.

The police fired thousands of tear gas canisters, but demonstrators seemed hardly to notice. Each time they were dispersed by barrages, they formed again on adjoining blocks and alleyways and closed in again with rocks and firebombs.

News services reported that clashes also continued yesterday in Pusan, Taegu and other provincial cities.

In the southern port city of Pusan, police reportedly fired tear gas at crowds of up to 15,000 protesters, who fought back with rocks and firebombs. Pusan police said that 265 officers were injured and that 58 demonstrators were detained.

In Taegu, in the southeast, protesters seized a city bus, overturned a fire truck and turned its water cannon on riot police, and set several police posts on fire.

Lesser incidents were reported in Inchon, Taejon and Wonju.

According to official police figures, 73,600 people staged rallies in 14 cities yesterday. That was in addition to 58,730 students on 78 universities and campuses. South Korean newspapers put the figures much higher. Police said they arrested 1,487 people during the day, and released 455 of them quickly.

Yesterday's events gave new evidence that the government of President Chun Doo Hwan, which values order in the streets above all else, is no longer able to maintain it and must seek some type of extraordinary solution.

Last weekend, the government gave serious consideration to emergency measures, all the way up to martial law. However, that approach was rejected over the weekend as party moderates argued that the protests would be better ended through conciliation.

Emergency steps would undercut the government's longstanding claims that it has put South Korea on a steady if slow course toward democracy. They would also be a major embarrassment abroad, especially in view of the 1988 Summer Olympics that are to be held in Seoul.

Wednesday night, President Chun Doo Hwan met with the ruling party's presidential nominee, Roh Tae Woo, and other senior party officials to examine the options open to them.

Officials here indicated they were exploring face-saving maneuvers by which the government would back off from its "irreversible" decision of April 13 to halt constitutional negotiations with the opposition. Opposition activists seek an amendment to provide for direct presidential elections.

"We really need a political solution to cope with the current student demonstrations," said a senior government official.

{President Reagan sent a letter to Chun within the past two days urging him not to overreact to the protests and calling for new talks with the opposition, Reuter quoted the New York Times as reporting Friday.}

The April decision was deeply unpopular, a point some ruling party officials now concede. "Reverse the constitutional decision" has been paired with "Down with military dictatorship" to make a chant that is constantly on the lips of demonstrators here.

Previously the government has said the talks can only be resumed after the Olympics. But now officials are talking of offering to resume them in the National Assembly at an unspecified earlier date and to put the reversal of the decision up for vote in a national referendum.

Korean newspapers depicted Roh as taking an assertive role in the search for a solution to the crisis, the worst challenge to Chun since he came to power in 1980 after a coup d'etat. "From now on, I will take the initiative in coping with political developments regarding the constitutional matter," Roh was quoted as saying last night.

Chun habitually maintains a regal distance from the public and day-to-day affairs of government. He has yet to comment publicly on the crisis.

Meanwhile, the ruling party was working toward a meeting between Roh and the president of the main opposition Reunification Democratic Party, Kim Young Sam.

The opposition was hinting, however, that it would put conditions on the meeting, such as an end to a two-month-old house arrest imposed on dissident figure Kim Dae Jung and the release of people arrested since the disturbances began.

It remained to be seen, however, whether the opposition would accept a deal with the government and, if it did, whether peace would be restored.

All of these political maneuvers took place before last night's upheavals in the streets, and it was not clear what effect the rioting would have on them.

The protests are being organized and carried out not by the opposition party but by radical students. Many would not be anxious to give up the unprecedented momentum they have generated in recent days and get only promises on the constitution.

Students stage protest rallies on Seoul campuses daily. Yesterday's upheaval was essentially the transfer of all those rallies into the middle of Seoul at one time.

It began around 4 p.m., when a rally was to start at a Presbyterian church to protest the police's use of huge quantities of tear gas, which have made large sections of Seoul unlivable in recent days.

Police barred entry to the church but people began massing in nearby streets. A sit-down strike was staged, blocking traffic. Soon the police attacked, using tear gas to break up the anti-tear gas rally.

Later, the action shifted to the area around Seoul's city hall and hotel district. The students' numbers quickly grew, reaching into the tens of thousands and putting the riot police squarely on the defensive.

Police attacked again and again, leaving passers-by squatting on the pavement immobilized by the gas. They used their standard nonlethal tactics, stressing the gas and such intimidation methods as formation charges and boot-stomping. Many protesters were injured, nonetheless.

Many of the skirmishes took place in rush-hour traffic, with grid-locked motorists getting first-hand views. In one place, police had to wait for a traffic light to turn green before they could charge across an intersection to attack students massed on the next block.

About 1,000 students, unable to reach the streets, gathered in an underground shopping arcade. "We have been fighting against military dictatorship since June 10," they chanted. "We will fight to the end."

One of the most dramatic engagements took place in the square in front of the Bank of Korea building. There protesters closed in on a beleaguered unit of about 80 military-uniformed riot police.

Overpowered, some of the men were beaten badly. Others were thrown into the pool of a fountain. Protesters ripped away their gas masks, shields, shotguns that fire tear gas and helmets, piled them on the street with a motorcycle and set them all afire with gasoline.

The policemen were freed and slunk away from the scene like a column of wartime stragglers. Some of the men could move only with both arms around comrades; others were soaked to the skin from the fountain pool.

Thousands of protesters, many wearing scarves over their faces to ward off tear gas, swirled around the fires to celebrate the victory. Soon, about 500 riot policemen advanced and fired one of the biggest volleys of gas seen in the crisis.