SEOUL, JUNE 14 (SUNDAY) -- For the fourth day in a row, South Korean riot police lost control of many of the streets in this city yesterday, with thousands of protesters defying close-order charges and clouds of tear gas and chanting "down with military dictatorship."

Wearing helmets and gas masks, police chased helter-skelter after demonstrators late into the night, sometimes pursuing them into private homes. In places, officers were showered with chunks of broken pavement and homemade gasoline bombs.

Meanwhile, Cabinet members with responsibility for internal security met this morning to discuss countermeasures to the disturbances, which are the most prolonged and serious in South Korea since 1980. There was no announcement of any decision.

"We want to control the situation just by using the police and civilian authorities," said Hyun Hong Joo, a ruling party spokesman. He suggested that the government's attitude now was to wait and see.

However, newspapers reported that officials had not ruled out declaring martial law if conditions deteriorate further.

The government is desperate not to employ lethal force, however. It did so in 1980 during demonstrations in the city of Kwangju, and more than 200 people were killed. That incident has remained the largest single barrier to stability and public acceptance of President Chun Doo Hwan.

With the 1988 summer Olympics set to open here 15 months from now, the government also is anxious to avoid steps that will create an image of repression and dictatorship.

Still, in private conversations, officials expressed concern that the street tactics were not working and that the police were growing tired after four days of operations.

Approximately 250 radical students today remained barricaded on the grounds of Seoul's Myongdong Cathedral, headquarters for the country's 2 million Catholics. The church was peaceful, in contrast to the violence flaring on streets around it.

No figures for arrests were released. But police were seen hustling large numbers of protesters into police vans and buses tonight, often kicking and punching the demonstrators along the way.

In many cases, neighborhood residents, angered by the gas that has invaded thousands of homes and workplaces, turned out to curse the police as they hauled protesters away.

The demonstrations began Wednesday to protest the death of a student during police torture and the nomination of ruling party chairman and former Army general Roh Tae Woo to succeed Chun as president.

Most of the protesters seem to be university students, who come to the task with seemingly limitless hatred for the government. Though they make up only a tiny minority of South Korea's 1 million university-level students, through brash tactics and often fanatical drive they have managed to keep their struggle in the public eye.

They fight police almost daily on the campuses. At least three have immolated themselves to protest Chun's rule.

The more elite a university here, the more radicals it is likely to have. They are young men and women who could have important jobs in industry and government for the asking but who instead have chosen lives that make arrest, interrogation and jail virtually certain.

They say they have no choice. "I cannot endure this country's political situation," said a 26-year-old political science student who was among the group at Myongdong Cathedral.

They see the Chun government as a military dictatorship that must be overthrown. The busloads of riot police deployed around Seoul and recent disclosures of police torture and controls on the press confirm these feelings.

Now they see Chun passing power to another former general, Roh, who helped him seize power in 1979.

Many of them accuse the United States, which maintains 40,000 troops in South Korea, of keeping Chun in power. Despite denials from Washington, they also believe the United States had a role in sending in the Korean troops that did the killing in Kwangju in 1980.

Their ideology is an eclectic mix. Some talk of "democracy" but are vague as to what it would mean in practice. Others are Marxists fighting for a communist state in South Korea. At least one of the Myongdong contingent called himself an anarchist.

The public here does not seem willing to support the students' often extremist tactics. Yet, with the Chun government widely disliked, many people seem to view them as idealists who have been forced into violence by government repression.

Education and scholars are deeply respected in Korea's Confucian ethics. There is a feeling that people with the intelligence and drive to make it into good schools must inherently be good.

At one point last night, about 50 students fought police on a busy thoroughfare about a half-mile from Myongdong. When a police bus closed in, disgorging dozens of plainclothesmen, the students threw two firebombs at it.

Moving quickly, police hurled gas grenades like rocks and tackled protesters wherever they could catch them. In one alley, police systematically kicked at the kidneys and chest of a protester as he lay on the ground. When police backed off, a local man came up and stroked the protester in encouragement.

The students' arrival at Myongdong Cathedral has turned out to be a stroke of tactical genius for them. Because the church is by tradition a sanctuary, the police have not gone in to arrest them. The students' continued presence there has inspired many of the protests taking place around it.

It also has brought the protection and moral force of the South Korean Catholic church. Priests and nuns have flocked to the church from around Seoul and are talking of forming human barriers to defend the students if the police raid the church.

"We support their spirit of protest, of democracy," said Augustine Ko, secretary to Cardinal Stephen Kim, leader of the country's Catholics.

The church is urging the students to forswear violence, he said, and has confiscated more than 200 gasoline bombs from them.