A four-hour barrage between North and South Korean troops early today apparently resulted from an attempted defection across the 38th Parallel armistice line by four North Korean soldiers. All four were killed or wounded by mines on their side of the 2 1/2-mile-wide demilitarized zone, according to South Korea.

It was the first major incident along the tense, 155-mile truce line since last September. Vice President George Bush is due in Seoul Sunday on the second leg of a five-nation Asian tour, but officials discounted the idea that the impending visit may have provoked the incident.

A spokesman for the American-led U.N. Command said "a serious fire fight" initiated by the North, during which hundreds of rounds of machine-gun and automatic-weapons fire were exchanged.

There were no casualties among the South Korean troops, the spokesman said.

According to the South Korean account, mine explosions followed initial firing from the North. The North Koreans then directed fire at a South Korean guard post, which returned fire, the spokesman said. At daybreak, the North Koreans were seen recovering four bodies from the zone.

A U.S. Embassy spokesman in Tokyo indicated that the incident might force a change in the vice president's itinerary for his two-day visit to South Korea but said that no details were immediately available.

The North confirmed that it suffered casualties, but said the battle was sparked by South Korean troops firing on a civilian police patrol. "The armed provocations of the South Korean puppet army caused casualties among personnel of our side on their routine patrol duty," said a report by the (North) Korean Central News Agency.

The incident is the latest in a 29-year pattern of intermittent violence along the DMZ in which 49 Americans and more than 1,000 Koreans have been killed. The heavily fortified truce line has separated communist North Korea from the South since the end of the Korean War in 1953. It comes at a time when military tensions have been rising in light of recent U.S. and South Korean assertions of a continuing, massive military buildup by the North Koreans.