Two scenes from South Korea tell a story of dramatic change and growing uncertainty:

The symbol of something new in Korean life -- the voluntary surrender of supreme national power -- is a small one-story marble building going up behind high steel gates 20 miles south of the capital. Although few citizens have ever seen it and virtually nothing about it has appeared in the local press, everyone knows it is the intended retirement office of President Chun Doo Hwan, who has promised to relinquish power voluntarily when his term of office is up in March, 1988.

Set amid spring flowers and a pear orchard, the building is the "guest house" of the Il Hae Foundation, which was established late in 1983 as a tribute to Chun. Unlike the current leader, the two previous long-serving presidents of the country, Syngman Rhee and Park Chung Hee, clung deperately to power despite rising discontent until the first was ousted by a student-backed revolution and the second was assassinated.

A warning of the political turmoil that may lie ahead in South Korea is the pop of tear gas cannisters exploding at an opposition political rally in Inchon. Several thousand students and workers are massed in the streets carrying banners and shouting anti-American, anti-government and anti-opposition party slogans when they hear the cannisters explode; the angry students rush the lines of riot police -- throwing bricks, rocks and Molotov cocktails.

Before my burning, tearing eyes the May 3 Inchon rally turns into a fullscale riot, the most serious internal disorder in six years. The police bring up a tank-like vehicle spewing a thick fog of searing "pepper gas," Korea's own contribution to crowd control. This only angers the demonstrators, who set fire to a car and spread the fighting over many blocks of the industrial port city where Gen. Douglas MacArthur made his daring landing in the early days of the 1950-53 war.

These two scenes -- one hopeful, one ominous -- are etched in memory from a seven-day revisit early this month to a country that seems desined to be the site of the next Asian political crisis following the triumph of "people power" over entrenched dictatorship in the Philippines. With Chun planning to step down and new forces rising among the opposition, the future of South Korea is up for grabs.

Given a history of 25 years of military-dominated rule and the fact that the generals control nearly all the guns, the odds are good that the future will belong to another military strong man. But such predictions are clouded by several new facts of life here: the broad unpopularity of the current military leader; the deep yearning for political expression after so many years of tight control; the emergence of a urban middle class that has risen out of povery and of a student generation that has no memory of the war.

The struggle for the future is being played out in a land where age-old temples and traditions survive amid a bustling, modern economy -- and where political institutions, having failed to keep pace with the economy, fit neither the old ways nor the new.

My first glimpse of Korea came in August, 1953, as I arrived for an eight-month tour of duty as a U.S. Army lieutenant. "Seoul is in ruins that are as complete as anything I can imagine . . . hardly a permanent building standing with four walls and a roof," I wrote in my little canvas-covered diary. My first impressions were of "miserable and pathetic" country, hungry children, lean-to hovels and a rugged, beautiful countryside dotted with thatch-roofed houses and walled villages.

When I returned as a journalist for the first time in 1966, economic development was getting underway and the people were becoming accustomed to the military-backed rule of Gen. Park. He had taken over in a coup in 1961 but, under heavy U.S. pressure, exchanged his uniform for a civilian suit and ran for president in direct elections. He won three times in reasonably honest national balloting. Korea in the mid-60's was no longer rubble-strewn and miserable; but it was poor, with a per capita income of $300 per year.

By 1972, when I returned to the area as Post bureau chief for Japan and Korea, Park was increasingly unpopular and repressive despite abundant signs of economic growth. In the fall of 1972 Park sent tanks into the streets under martial law, scrapping the constitution and direct elections to keep himself in power. I went to Seoul at least 25 times in my three-year tour. The thing that impressed me most toward the end was that Park, though he controlled the guns and police, was so fearful that the halls of his own Blue House were emptied when he walked through them as a precaution against assassins.

By mid-1980, when I went back to Korea again, Park had been gunned down by his own secret police chief across the table at a private dinner and Gen. Chun, once a young protege of Park, was the dominant figure in government after leading a military coup. There was a sense of dismay among Koreans that one military rule was succeeding another. Chun, whose position was shaky, was bidding for U.S. approval which he finally obtained as the first White House state visitor at the beginning of the Reagan administration.

The situation which I found on this month's trip is an outgrowth of trends that were evident before. Economically the country has continued to grow dramatically, emerging in the past decade as a "middle power" of global importance with a per capita income of about $2,000 per year, which is officially projected to rise to $3,500 in five years' time. But political growth has not kept pace with the economy.

As in the past, political expression continues to be stunted by secret police and military controls and severe restrictions on the press. But people seem less inclined to accept authoritarian rule now that there is enough to eat and wear. "Below $1,000 per year income, if you eat you won't complain much," said Sa Kong Il, a presidential economic adviser who believes that the $2,000 stage is "an awkward period" of national development. One of the country's leaders, looking out at the Seoul skyline from a 35-story luxury hotel, mused that impatience and even radicalism grow naturally in the shadow of such skyscrapers.

The dichotomy between rapid economic growth and slow political development results in large part from military domination of politics, which arises in turn from the continuing high level of military tension in the bitterly-divided Korean peninsula. The permanent showdown with the communist north, moreover, has been used to justify suppression of dissent or opposition on the grounds of national security.

Korea remains one of the world's most dangerous powderkegs. Heavily armed North Korea, which has recently acquired more modern weaponry through increasingly close relations with the Soviet Union, has a powerful army of nearly 900,000 troops (by U.S. estimate) across a thin demilitarized zone about as close to Seoul as Rockville is from downtown Washington. In response South Korea maintains a heavily-armed force of about 500,000 troops, which is far larger and more powerful than it would be in the absence of the external threat. In addition, some 40,000 American GI's remain on duty nearly 33 years after the 1953 armistice, as tangible evidence of a U.S. military commitment to the last non-communist foothold on the mainland of East Asia.

The problem of political transition in the South begins with the weakness of democratic institutions. Although the country has a facade of civilian rule, including civilian ministries and a sometimes fractious but essentially weak National Assembly, the real authority is Chun, a few close aides and a behind-the-scenes ruling group of a dozen or so generals, like Chun four-year graduates of the Korean Military Academy. The generals dominate military decisions and are believed to have considerable influence on many three times in reasonably honest national balloting. Korea in the mid-60's was no longer rubble-strewn and miserable; but it was poor, with a per capita income of $300 per year.

By 1972, when I returned to the area as Post bureau chief for Japan and Korea, Park was increasingly unpopular and repressive despite abundant signs of economic growth. In the fall of 1972 Park sent tanks into the streets under martial law, scrapping the constitution and direct elections to keep himself in power. I went to Seoul at least 25 times in my three-year tour. The thing that impressed me most toward the end was that Park, though he controlled the guns and police, was so fearful that the halls of his own Blue House were emptied when he walked through them as a precaution against assassins.

By mid-1980, when I went back to Korea again, Park had been gunned down by his own secret police chief across the table at a private dinner and Gen. Chun, once a young protege of Park, was the dominant figure in government after leading a military coup. There was a sense of dismay among Koreans that one military rule was succeeding another. Chun, whose position was shaky, was bidding for U.S. approval which he finally obtained as the first White House state visitor at the beginning of the Reagan administration.

The situation which I found on this month's trip is an outgrowth of trends that were evident before. Economically the country has continued to grow dramatically, emerging in the past decade as a "middle power" of global importance with a per capita income of about $2,000 per year, which is officially projected to rise to $3,500 in five years' time. But political growth has not kept pace with the economy.

As in the past, political expression continues to be stunted by secret police and military controls and severe restrictions on the press. But people seem less inclined to accept authoritarian rule now that there is enough to eat and wear. "Below $1,000 per year income, if you eat you won't complain much," said Sa Kong Il, a presidential economic adviser who believes that the $2,000 stage is "an awkward period" of national development. One of the country's leaders, looking out at the Seoul skyline from a 35-story luxury hotel, mused that impatience and even radicalism grow naturally in the shadow of such skyscrapers.

The dichotomy between rapid economic growth and slow political development results in large part from military domination of politics, which arises in turn from the continuing high level of military tension in the bitterly-divided Korean peninsula. The permanent showdown with the communist north, moreover, has been used to justify suppression of dissent or opposition on the grounds of national security.

Korea remains one of the world's most dangerous powderkegs. Heavily armed North Korea, which has recently acquired more modern weaponry through increasingly close relations with the Soviet Union, has a powerful army of nearly 900,000 troops (by U.S. estimate) across a thin demilitarized zone about as close to Seoul as Rockville is from downtown Washington. In response South Korea maintains a heavily-armed force of about 500,000 troops, which is far larger and more powerful than it would be in the absence of the external threat. In addition, some 40,000 American GI's remain on duty nearly 33 years after the 1953 armistice, as tangible evidence of a U.S. military commitment to the last non-communist foothold on the mainland of East Asia.

The problem of political transition in the South begins with the weakness of democratic institutions. Although the country has a facade of civilian rule, including civilian ministries and a sometimes fractious but essentially weak National Assembly, the real authority is Chun, a few close aides and a behind-the-scenes ruling group of a dozen or so generals, like Chun four-year graduates of the Korean Military Academy. The generals dominate military decisions and are believed to have considerable influence on many non-military decisions.

The generals have become used to the prerogatives and perks of power and are anxious to protect their privileged status. Yet they realize, according to one of the few outsiders who is in position to know their mind, that they must contend with rising public demand for civilian rule. And they understand too that Chun's day is drawing to a close.

The central issue in South Korea today, in view of this, is the question of how a new leader is to be selected or elected. Since the campaign for president must start sometime next summer or early fall if there is to be one, only about a year of debate and decision remains before this crucial question should be settled.

Chun, the military leaders and people close to them have insisted on the method devised by Park to keep himself in power, which was continued in Chun's 1980 constitution: indirect presidential selection by an easily-controlled convention of 5,000 citizens elected from the nations' wards. This system would maximize the chances for another military figure, such as Chun's friend and military academy classmate, Gen. Ro Tae Woo, currently president of the ruling Democratic Justice Party, or someone else selected by or at least endorsed by the military.

The major opposition party, on the other hand, is insisting on a return to the pre-1972 practice of direct popular election of the president, calculating that either the controversial Kim Dae Jung, the less militant Kim Young Sam or some other opposition figure would be the public's choice at the ballot box.

The main leverage of the opposition, which has only a modest position in the national assembly and little access to the controlled press, is public pressure exerted through mass demonstrations and petition drives. But while the traditional activism of Korean students is an asset in exerting this leverage, radicalism or violence places the moderate opposition in a difficult position.

The opposition's position will be enhanced over the next several years as Korea heads toward the 1988 Olympic Games, which will be held in Seoul. With Korea in the media eye as never before, the opposition feels freer to act, and the government appears wary of cracking down on demonstrators.

The May 3 Inchon rally, which exploded in violence between demonstrators and riot police before speechmaking could begin, severely embarrassed the opposition. Opposition party leaders were dismayed by fighting in the streets and appalled by the anti-American and anti-opposition party slogans carried and shouted by student demonstrators.

The major slogans of the student groups, three student leaders told me, are "Drive Out American Imperialism Hindering National Self-Reliance," "Withdraw Nuclear Bases Threatening National Survival" and "Drive Away U.S. and Japanese Capital Forcing Recession and Unemployment."

This anti-Americanism is a sharp break from a past in which the United States played the role of savior and role model. The United States drew the dividing line between North and South at the end of World War II, intervened militarily to repel the North Korean attack in 1950-53, aided the country economically throughout most of its remarkable growth spurt and has continued for three decades to provide a nuclear umbrella and other security guarantees that may be essential to South Korea's continued survival.

Nearly everyone I questioned on the matter, Koreans and Americans alike, said serious anti-Americanism began with a celebrated incident of six years ago this month -- the brutally-suppressed uprising in the provincial city of Kwangju in which about 200 people were killed as Chun cemented his power. Seoul National University students surveyed in a campus poll last year named the Kwangju incident as the single most unfortunate thing that has happened in Korea since 1945 -- more serious to them than the Korean war, in which about 5 million people were killed or died of war-related causes, but which the students do not remember.

Because of Kwangju, Chun is seen as having come to power with blood on his hands and since he has never acknowledged error or apologized he cannot be forgiven. For many Koreans the United States was partly responsible as well, because of the widepread belief that the U.S. command released Korean forces from front-line duty to suppress the disorder. In fact, the Korean generals were only required to notify the U.S. command when moving troops.

U.S. officials have insisted for years that they had nothing to do with the Kwangju suppression and that it was never the U.S. intention to contribute to the killing of Korean civilians, but a clear and emphatic official statement along these lines has been lacking. Repeated appeals by the U.S. Embassy in Seoul for an official statement disassociating the United States from Kwangju have been vetoed in Washington, evidently because of a desire not to embarrass Chun.

A keen sense of disappointment about the recent U.S. role was evident in conversations with Koreans I have known for many years. One of them summed up this view by saying, "We remember Americans as the ones who saved us from the North and helped us out of poverty. We wore U.S. Army blankets for coats against cold winters in this country, and we cheered the U.S. ambassador's car as it moved through the crowds to tell Syngman Rhee he had to step down in the interest of democracy. But since there has been Kwangju and you've stuck close to Chun, and we have a really different feeling."

Whatever influence the United States has in South Korea -- and Washington officials insist it is less than most Koreans believe -- will be severely tested as the country sorts out its political future in the coming months. The U.S. Embassy in Seoul has been counseling compromise and moderation. But Shultz' public statements during his recent trip to Seoul seem to have made that role more difficult by seeming to endorse all that Chun is doing, while saying harsh things about the opposition.

History and geography give the United States a huge stake in South Korea as it approaches a crucial transition. But the Reagan administration's policy, at this point, seems to be little more than "Back Chun." This approach hasn't been adequate or successful in the recent past, and it may be courting disaster in Korea's increasingly uncertain future.