N. Korean Infiltration Cited in Fatal Encounter : Asia: After South’s forces kill accused agent from North, Washington and Seoul plan joint protest over incursion.

U.S. and South Korean forces concluded Tuesday that an attempt by the North Korean army to infiltrate the South spurred a shooting incident near the Demilitarized Zone, and they agreed to protest jointly to Pyongyang, a U.S. spokesman said.

The incident, in which a frogman believed to be a North Korean agent was shot to death, underscored the fact that the North and South remain at each other’s throats even as U.S. relations with North Korea have improved, said United Nations Command spokesman Jim Coles.

“But it would be inappropriate to say that the incident represents an escalation of tensions,” Coles added in a telephone interview.

Although the shooting was the first fatal encounter in more than three years, the North Korean army “constantly probes the frontier and sends people across the Demilitarized Zone,” which has separated North and South Korea at the 38th Parallel since the Korean War in the early 1950s, Coles said.

South Korea’s Defense Ministry echoed that judgment. Noting that only two days’ worth of food supplies were found at the scene of the shooting, its spokesman said North Korean agents were probably only “on a reconnaissance mission to check the readiness of the South Korean military rather than aiming to stage a surprise attack.”

The joint U.S.-South Korean protest will be made to the Military Armistice Commission in the truce village of Panmunjom “as early as possible,” Coles said.

A North Korean agreement last year to halt its suspected nuclear weapons program in exchange for receiving two nuclear power plants under a U.S. guarantee has opened the doors to increasingly regular contacts between Washington and Pyongyang. But the North and South have remained at loggerheads despite a requirement in the U.S.-North Korea agreement that Pyongyang open a meaningful dialogue with Seoul.

In a rare move Tuesday afternoon, the South Korean Defense Ministry allowed reporters to visit the scene of the shooting at the Imjin River.

South Korean army Cpl. Chung In Jae, 22, told the group he heard “a strange sound” around 1:20 a.m. at the bottom of a cliff where he was standing guard. He and an army private investigated, their vision impaired by a thick fog.

About 50 minutes later, a figure suddenly emerged, Chung said, and raised his arm as if to throw a hand grenade. Chung said he fired his rifle “almost point-blank,” and his teammate threw two hand grenades.

Only after the sun came up nearly four hours later did a search team discover a body, a pair of diver’s fins, two M-16 rifles and two vinyl bags. In the bags were pistols, ammunition, two Japanese cameras, chocolate made in China, underwear made in Japan, medicine, food and fake South Korean army uniforms.

Reporters were shown the body of a man in his early 20s with curly hair--unlike the crew-cut style of South Korean soldiers--who had been shot in the head.

South Korea’s Defense Ministry today said a second suspected North Korean agent survived the shooting and was spotted walking toward a North Korean guard post after coming ashore on the other side of the river Tuesday afternoon.

The suspected infiltrators were believed to have swum in from the Yellow Sea on a high tide that flows inland.

It was the first time since 1992 that an armed infiltrator was reported killed. In May, 1992, three armed North Koreans were shot to death near the Demilitarized Zone, according to a South Korean announcement that North Korea called a fabrication.

* Chi Jung Nam of The Times’ Seoul Bureau contributed to this report.

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Frogman Killed

The shooting occurred near the Demilitarized Zone that has separated North and South Korea since an armistice ended the 1950-53 Korean War. The frogman was believed to have swum up the Imjin River from the Yellow Sea.