SEOUL -- Lee Ki Ho, then 24, knew the North Korean Communists had captured his city when he found three Seoul policemen shot dead on the street in front of his watch repair shop.

Kim Young Chul, then a high school freshman, learned about the invasion when leftists who had just been freed from jail, their shaved heads glistening, ordered him into the streets to welcome advancing North Korean tanks. "We raised our arms and shouted 'manse' -- May you live 10,000 years," said Kim, now a successful businessman and author. "The dark 90 days began then."

Forty years ago on Monday, the Korean War began. For the United States, the three-year war was a bloody and frustrating conflict far from home that set the nation firmly on a path of military buildup and Cold War confrontation. For Koreans, it was a fratricidal war that destroyed the nation and led to its formal partition. Even today, the peninsula remains perhaps the most dangerous region of confrontation left over from the Cold War.

The distrust that still afflicts relations between North and South is rooted in the three-month North Korean occupation of this city that started with the invasion and ended when Gen. Douglas A. MacArthur's troops entered the city Sept. 28, 1950.

The story of that occupation is a tale of terror -- of sons shot in the streets at "people's courts" and left to rot in the summer heat; of husbands marched north in chains, never to be seen again; of hunger and cruelty, hiding and constant fear.

Most of those who survived that summer are united even today in suspicion and hatred of the North Korean regime, and in gratitude to the Americans for liberating Seoul.

"These things hold us together," said Lee Hong Koo, now a close adviser to President Roh Tae Woo. Lee spent that summer hiding in a basement. "People over 50 -- we share a feeling about national security."

But the story of that first summer is also a tale of ambiguities and shifting loyalties. While most Seoul residents feared the Communists, others welcomed them; and while most cheered the Americans' arrival three months later, some willingly followed the North Korean army in its retreat north.

Even today, many Koreans prefer not to recall the compromises and adjustments they made during the first stage of that bloody war. For them, only one thing is sure: It was the civilians who bore the brunt of the attacks, whether by U.S. warplanes, North Korean artillery, partisan guerrillas or South Korean police.

"It was hell," said Oh Hae Ju, who was dragooned into the "People's Volunteer Army" at age 17, but escaped two days later. "People were afraid of both sides."

The first reaction to the North Korean invasion was disbelief. Korea had been divided since 1945, when the Soviet Union occupied the North and the United States the South after World War II. Through much of those five years, U.S. and South Korean forces battled leftist guerrillas in the South, while the two sides skirmished along the border.

When the artillery was booming just beyond Seoul's northern hills, many Koreans still could not believe the truth. They chose instead to place their faith in a radio message by President Syngman Rhee, who assured them that the South Korean army was in control.

In fact, by June 27 the army was fleeing in disarray. A disgusted MacArthur said, "I haven't seen a single wounded man yet" when he flew in from Tokyo for a brief inspection of the retreating South Korean troops. Rhee, too, had moved south, leaving only his tape-recorded voice on the radio to soothe his citizens.

By the time Kim and his family tried to flee, the panicky South Korean army had blown up the only bridge across the Han River, leaving Seoul and its citizens at the mercy of the North.

Political cadres quickly set about organizing "People's Committees," rooting out "reactionaries" and recruiting young men for their army. Anyone associated with the South Korean government hid in storm sewers or basements or attics; soldiers who had been left behind, darkened their foreheads with ashes to hide the tan lines left from their military caps.

Lee Ki Ho, now 64, recalled that the North Koreans first tried propaganda and persuasion. "They spread the word there would be a free movie show, and many people went to the theater," he said.

"In the middle, they stopped the picture and cadres came out and started talking about the honor and glory of the North Korean army. Some young men in the front row jumped on the stage, shouting, 'I joined the People's Volunteer Army,' and soon many young men were joining them as if under a spell. Then the leader said, 'Left face! Forward march!' and they were gone. It was like sorcery."

To persuade everyone they were winning the war, Kim recalled, the North Koreans paraded U.S. prisoners of war through the city, forcing them to walk barefoot over the hot asphalt, their boots tied by shoelaces and hanging around their necks. "They looked worn out, heads down. I thought, 'This must be the end,' " Kim said.

But Lee said the North Koreans' methods were often less subtle. "They killed people like we kill flies," he said.

One afternoon he came across a crowd in front of a downtown theater. "This man is a reactionary," a cadre shouted of a bound prisoner. "Shall we kill him?" The crowd of North Koreans and sympathizers roared approval. The man was shot, dragged to a ditch in the road and covered with a burlap sack.

Lee also lost a friend who entered a People's Committee office seeking to recover a cigarette lighter that a North Korean officer had taken from him. "They took him to the basement and shot him," said Lee, who retired from the mining business last year. "There were so many people killed mercilessly. It's hard to explain all those bad things."

By late July, the North Koreans were seizing almost any able-bodied male they could find wandering the streets or hiding in houses.

Oh, who took advantage of a U.S. strafing raid to escape two days after being drafted, said a cousin drafted at the same time was not so lucky. There has been virtually no communication between ordinary citizens of North and South Korea since the war ended in 1953, and Oh has no idea if his cousin is alive today.

Yet not every North Korean was ruthless. Chu Tong Ful, now in the shipping business, recalled the soldier who came looking every week for Chu's father, a newspaper editor who had been branded a reactionary. Each time, his father would hide beneath the floorboards or behind the cupboard, yet the soldier never looked too hard, perhaps because he came from the same province as Chu's mother. "My father's life belonged to that man," Chu said. "We don't know why he never took my father."

By September, there was almost no food in Seoul; Chu's mother would roam the countryside seeking to trade her clothing for barley to make gruel. The North Koreans, preparing to retreat, set fire to much of the city; the Americans, advancing from Inchon, bombed most of the rest. "I don't know how anyone survived there," recalled John Rich, an American reporter who reached Seoul in October. "The city was incredibly beat-up, just flat and rubble."

As they pulled out, the North Koreans and their sympathizers sent Seoul through one more spasm of terror, shooting hundreds and rounding up intellectuals, poets and others for a forced march north. At the same time, many North Koreans were left behind. Oh recalled wounded soldiers who starved to death, too weak to move and ignored by local citizens.

The Americans and South Koreans and their allies pushed north to the Manchurian border, then were pushed back down again when China entered the war. Once again, South Koreans had to flee, this time in bitter cold. Finally the front moved back to the original 38th Parallel, where the war continued in deadly stalemate for two more years. By its end, 33,629 Americans had been killed and more than 100,000 injured. Millions of Koreans were casualties; virtually every family was affected.

"I can't say the bitterness is gone," Lee Ki Ho said in a Seoul coffee shop. Still, 70 percent of South Korea's population has been born since 1953. Ten years from now, South Korea's leaders will almost surely be people who did not fight in the war.

"People of my age worry about the younger generation, people younger than 40, who didn't experience the war," Lee said. "I don't know if they realize what communism is really like, how badly they treated the people."