A South Korean scholar was attempting to explain to a foreigner this week how Park Chung Hee had ruled this country so long and why there was such genuine shock and mourning over his assassination one week ago.

"To understand," he said "you would have to have known the chaos of 1960."

That was the year of turmoil here, the last of a lot of bad years in this century for Koreans. There were massive student riots and many were killed. Syngman Rhee, the strongman president had resigned. There was a year of instability and more economic ruin, when a subsistence diet was a luxury.

"You have to understand," said the scholar, "that we would not have minded having Kim Il Sung if he had guaranteed three meals a day."

Instead of Kim Il Sung, the North Korean Communist leader, South Korea got Park Chung Hee as a result of a military coup in 1961 and he ruled until last Friday night when he was assassinated. It was a remarkable reign, the longest of any Asian noncommunist leader except for Singapore's Lee Kuan Yew.

It was held together in the last years by fear and terror. Dissidents were spied upon and relentlessly intimidated. Political prisoners were tortured. One political opponent was kidnaped abroad and later imprisoned. He is still under house arrest. Another was expelled from the National Assembly for his critical remarks.

Even his loyal aids were often terrified. Early this year, a foreign reporter was chatting with one of Park's more sophisticated executives. He is a man of broad learning and considerable detachment, regarded by outsiders as one of the few in Park's government who enjoyed a sense of personal security.

Suddenly the special telephone linking his office with the president's rang on a desk 15 feet across the room. The official bounded to his feet and raced like a frightened rabbit to grab the phone before it stopped ringing. Throughout the conversation that followed, he stood stiffly at attention.

In the last years, the signs of paranoia appeared. A half-mile from the Blue House, the presidential mansion, windows in hotels are taped or shaded to obstruct the view of anyone trying to see where the president lived. When he appeared in public, guests had to be seated in their places for an hour before he arrived.

An Asian who has lived in South Korea for many years recalls an unusual experience at a luxury mountain lodge almost exactly one year ago. A worried hotel manager came to his door and asked him to vacate his room immediately. The same request was made of the couple next door and all of the guests in the 60-room lodge. Downstairs in the lobby the reason became clear. Park's bodyguards were clearing everyone out to make way for a one-night visit of the president and his daughter, Keun Hae.

Why was it all tolerated? Park was the least charismatic of rulers, a man who outwardly seemed devoid of any personal charm. In public appearances and in the photographs he permitted to be published he was stern and grim.

Foreigners who saw him operate with subordinates say he appeared to behave like some austere lord of Korea's Yi dynasty, always demanding, never smiling. He public statements deplored frivolity and spoke always of duty.

One reason Park's grim regime was tolerated is the South Koreans' overriding fear of the North. There is hardly a family in South Korea that did not have some relative killed or wounded in the Korean war that ended in 1953 with a division of the country. They have lived in daily fear of another attack and preventing that attack from beginning is their greatest concern.

There is a deeper but more elusive reason. Park gave most South Koreans a sense of stability and national identity they had not known in this century. Many foreign observers have commented on the deep strain of pessimism about themselves as a nation that runs through almost all South Koreans.

There is a feeling, they have noted, that without force from above South Korea might disintegrate. One government official recently commented that despite all the trappings of democracy -- elections and political parties and a National Assembly -- South Koreans think they cannot govern themselves. Real dissent is too dangerous to be tolerated, he said, adding: "We are not mature enough."

The pessimism includes a conviction that, in a crunch, South Korea's allies cannot be trusted. That conviction grew even stronger with the American defeat in Vietnam and the subsequent signs that the United States, chief protector of South Korea, was pulling out of Asia. President Carter's initial plan to withdraw U.S. combat troops from South Korea heighted the suspicions. It made no difference how many times the United States promised to keep its security commitments here.

'The Koreans," said a former ambassador to Seoul, "have an infinite capacity for absorbing reassurance."

The pessimism about self-government and foreign powers is not all the result of imagination. There is plenty of history in the past century to support it. Korea finished the 19th century under a corrupt dynasty and succumbed to Japanese colonization, after the Americans signaled disinterest in the region, in 1910.

For 35 years the Japanese methodically attempted to pull South Korean culture out by its roots: even the native language was banned in schools. After the occupation ended in 1945, there was widespread poverty and then a destructive war with the North.

Park, a general, emerged from the military coup of 1961 as leader of a ruined country. Throughout the 1950s' the South had survived on U.S. economic aid. The entire decade was one of zero economic growth.

Somehow, under his reign, it all began to change. Following the Japanese model, the government began an economic boom by emphasizing exports of consumer goods textiles, shoes, toys, cheap electronics. Park secured American technical aid and international loans and installed technocrats trained at American universities in key economic departments. Suddenly the exports took off.

By the time Park died the economic miracle was a fact. South Korea, for a decade, had a consistent growth annual rate of 10 percent or more. It now builds and ships entire plants to the Middle East and sells automobiles in Latin America, Africa and Europe. Per capita income is now high enough that South Korea soon will emerge to become officially recognized as a developed country.

Much of the credit goes to the technocrats who directed it all, managers who are recognized around the world as wizards in the art of pulling an underdeveloped country up out of poverty. Yet many foreign observers have insisted it would not have happened without Park.

One Western economist who was permitted to observe the inner workings of South Korea's boom says to an extent that surprised him Park was making key decisions in the early 1970s. Park set the targets and insisted on weekly measurements to determine whether they were being reached. If a railroad bridge were not finished on time, the economist said, the minister in charge had to explain why.

That economist had also had experience in India and he thought the comparison revealing. India, he said, had had similar infusions of foreign aid and used its foreign-trained technocrats. "And India," he said, "is still India."

The result in this decade is an expanding middle-class with a large stake in Park's era of prosperity. There also has developed a kind of unstated trade-off between the economically prosperous and Park's regime: leave politics to Park and the making of money to us.

The assassination last week triggered a revival of all the old fears of disorder and poverty: student protesters marching, soldiers responding with violent repression, an economy again in ruins.