Han Won Song returned to the faculty of Seoul National University yesterday after a four-year course of studies in what he now feels able to joke about as the "college of real society."

A professor of political sociology, Han was dismissed in 1976 for writings deemed critical of the South Korean government. Since then, he has been arrested five times for questioning about political statements urging the revival of democracy. Barred from teaching, he earned a living as editorial adviser for Christian publications.

Yesterday was his homecoming. The students applauded and shouted greetings when he entered the classroom. "I told them I had spent four years in the college of real society," he said. "I will be lecturing a lot about that."

Hans return is part of a board revival of campus liberties in South Korean 4 1/2 months after the assissination of President Park Chung Hee, whose authoritarian, administration had strictly limited academic freedom.

Beginning in 1973, the country's colleges were stripped of their more outspoken professors and restive students. Lectures were monitored by spies placed on campus by the Korean Central Intelligence Agency. Students were classified according to their dissident thoughts and hundreds were expelled.

The new civilian government has been moving gradually to dismantle vestiges of the old regime. Police and KCLA agents have been removed from campus autonomy in supervising students. Academic freedom is gradually being restored, although it remains to be seen how extensively it can be used.

Most visible of all reforms is the return of professors and students, many of them recently freed from prison and granted amnesty. The Ministry of Education estimates that since 1973, about 800 students had been expelled and 39 professors ousted. It says 639 students have been reinstated and 25 professors rehired.

The reforms who hastened to an awareness that South Korea's volatile students might take to the streets in protests this year unless changes were made to assure more freedom on campus.

Kim Ok Gill, the new minister of education, is regarded as one of the more reform-minded members of the present interim government. One of her actions abolished a bureau that funneled money to certain professors and student groups in exchange for their support. Dissidents had long believed the money was used to pay informants who reported on students and professors suspected of antigovernment sympathies.

In one controversial area, the government has been only partly successful in defusing student objections. The Student Defense Corps, which students resented as an instrument of government control, has been partly dismantled. Its leaders will now be elected by student members instead of appointed, but there is campus agitation to have it renamed or abolished.

The government's original plan to abolish the student military corps was modified at the insistence of the martial law authorities who have wielded influence over civilian matters since Park was assassinated on Oct. 26.

Some students also object to the continued presence on campus of progovernment professors they suspect were placed on faculties by Park's administrators to keep tabs on dissident students and professors.

Campaigns to oust them are opposed by several returning professors, who worry that new witch hunts might sweep the campuses and cause widespread unrest.

"I am asking my students not to push them too hard and to be very careful not to hurt them," said Kim Dong Gill, a history professor at Yonsei University who was reinstated last December.

A scholar who specialized in the life of Abraham Lincoln, Kim is typical of many professors who were dismissed and imprisoned for antigovernment activities. He was fired in 1974 and contends that several students were tortured into saying he had supported campus uprisings.

Kim spent a year in prison where he lectured jailed students on world history and English poetry. "It was really a rather joyful experience," he recalled.

After his release from prison, Kim was under house arrest at times and was followed whenever he moved around the city. Detectives watched homes and meeting halls where he lectured to religious groups.

It is not clear how much teaching freedom will be permitted. Professors interviewed this week said no firm guidelines have been established. The teaching of Marxist theory, for example, has been impossible and whether it will be revived is not known.

Professor Han has lost no time in testing the new boundaries. In his first lecture since returning to the Seoul National University campus, he compared past impediments to teaching sociology to problems encountered by German social scientists in Nazi Germany.

"I told them that the study of socialolgy could not grow under an authoritarian regime," Han said. "In some ways the German sociologists were more free, because they could flee the country and teach in exile."

Travel outside South Korea was and still is strictly restricted and Han had to turn down a 1977 Fulbright fellowship to study in the United States because the government would not give him permission to go abroad.