WORLD NEWS TOMORROW KOREA, South Korea — “Some people think I’m crazy,” says Kim Jin-cheul, a Christian preacher who is convinced that North Korean soldiers are digging tunnels that extend under the capital of Seoul, 30 miles from the border, and have reached this town, 10 miles farther south, where he ministers to a congregation of nine families.

“Imagine hordes of crack North Korean troops streaming out and taking the whole city hostage!”

Imagine. Mr. Kim, 47, is one of a small but dedicated band of South Koreans who have been hunting for North Korean “invasion tunnels” for years, some for decades. Only four tunnels have ever been detected, all between 1974 and 1990 and all near the border. Not one has been found since, despite thousands of drilling operations conducted not only by the South Korean military but also freelance prospectors like Mr. Kim.

Although broadly dismissed as cranks, the private tunnel hunters tap into the source of one of South Koreans’ greatest fears about North Korea: its penchant for taking its war preparations underground, a reaction to the leveling of its military installations by United States air power during the 1950-53 Korean War.

A reminder of that subterranean threat came in May, when Brig. Gen. Neil H. Tolley, commander of United States Special Operations in South Korea, was quoted as saying at a conference in Florida that North Korea is thought to have constructed thousands of tunnels and other underground military facilities. These include 20 partially subterranean airfields and thousands of underground artillery positions. But officials, while stating that they cannot be sure where North Koreans have dug, say that they believe the tunneling has been limited to the North.

The South Korean Defense Ministry said it remained on the lookout for possible tunnels by drilling along the border and applying advanced sound-detecting and other equipment.

“We don’t ignore even the smallest signs of a possible tunnel because these tunnels could determine the outcome of a war and our country’s survival,” it said in a faxed response to a question about the tunnel hunters’ accusations that the ministry is not doing enough.

But it also said it was technically impossible for the North to dig tunnels as far south as people like Mr. Kim say.

“Most of those who claim to have found a tunnel are using unscientific methods,” it said. “All their claims have proved false.” The tunnel hunters include retired military intelligence officers, Christian pastors asserting that God has revealed a tunnel location, and even a near-blind Roman Catholic priest who says he discovered 17 invasion tunnels with a dowsing rod. No one else has verified any of the claims.

The tunnel scare began in 1974, when South Korean border patrols saw steam shooting up from the ground. Drilling revealed a tunnel that had reached about five-eighths of a mile south of the border. To this day, North Korea denies having dug any such tunnels.

The South Korean military maintains two of the tunnels for tourists to warn younger generations about the danger it says North Korea still poses six decades after the Korean War ended in a truce.

The narrator in a video shown to visitors intones: “Listen carefully. You might hear a faint noise from a motor running in the dark underground.” He continues, “As long as underground provocations continue, there can be no true peace above the ground.”

Few take this exhortation more to heart than the Rev. Lee Jong-chang, 78, a Roman Catholic priest and veteran tunnel hunter. “I am doing this work so that we won’t have another war and nobody will be hurt,” he said.

Father Lee said he was helping villagers find ground water with dowsing skills he had learned from a French missionary when the government asked him and other civilian experts to join the military’s search for tunnels in 1974. He was awarded a presidential medal for helping find the second tunnel, in 1975.

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