SEOUL, JUNE 16 -- South Korean students kept up strong pressure on the government today with a new wave of rallies, some of which erupted into exchanges of tear gas and firebombs.

Although demonstrations abated in central Seoul, considered the most important indicator of the degree of unrest, 6,000 protesters fought riot police, burned a police bus and set up barricades in the southern port of Pusan, The Associated Press reported. Later, 300 students occupied Pusan's nine-story Roman Catholic center and continue to hold it hours later.

More than 40,000 students from 57 universities also took part in protests today, according to South Korea's Yonhap News Agency. In the southern port city of Chinju, radicals were reported to have attacked two police posts, smashing windows.

The demonstrators were seeking an end to the government of President Chun Doo Hwan, which they consider a military dictatorship.

The daily Chosun Ilbo reported that nationwide a total of seven police posts and one checkpoint were attacked with firebombs. Two local offices of the ruling party in the city of Taejon were attacked and partly burned.

New details also reached Seoul of an unusually large and violent wave of student-dominated protests in provincial cities yesterday.

In Chonan city, for instance, about 3,000 students were reported to have taken to the streets, attacking the local office of the ruling party and a police post with rocks and firebombs.

Central Seoul, however, was largely back to its normal state today, except for the continued presence of squads of riot police on street corners and an antigovernment rally by about 1,000 people on the grounds of the Roman Catholic Myongdong Cathedral.

The protesters chanted slogans and sang the national anthem but drew only minor attention from passers-by.

Although demonstrations were continuing on campuses and in many provincial towns, observers saw significance in the fact that they had died down in central Seoul.

The government had been deeply concerned about the protests in the center of the capital and the participation of ordinary citizens, a highly unusual occurrence.

Fire trucks washed residue of tear gas off the capital's streets. Food stalls and restaurants that cater to nighttime strollers reopened for business after five days of disturbances around the cathedral.

Yesterday, about 200 students who had taken refuge in Seoul's cathedral for five days were bused out after police promised not to arrest them. Their presence there had sparked a chain of protests in the streets around the church.

Authorities had hoped that getting the students out would completely end the protests there. But tonight's rally indicated that students will try to maintain their foothold at the cathedral.

Priests at the church seemed dismayed by the prospect of hosting more protesters indefinitely. The Rev. Ri Ki Jung, assistant priest of the cathedral, said he hoped they would go home for the night.

Meanwhile, new hitches developed in political negotiations that are supposed to help solve the crisis, which began last Wednesday as the ruling party nominated its chairman, Roh Tae Woo, as a presidential candidate.

Representatives from the ruling and opposition parties had met yesterday to seek convening of a special session of the National Assembly to discuss the crisis.

Today, however, the opposition Reunification Democratic Party said it would boycott the session unless the government grants certain conditions.