A bitter propaganda war - carried on mostly over the airwaves, but also by means of balloon bombs and loudspeakers on the border - rages on between the Koreas nearly 30 years after arms were officially laid down. Many of the broadcasts are jammed, or too crude to be effective. The broadcasts may be a danger to peace - or just a safety valve to let North Korea blow off steam.
A Korean family was enjoying a quiet evening watching television recently when an explosive device crashed through the roof of its house in the suburbs of Seoul.
Among the debris of charred batteries, balloons, and propaganda leaflets was the message, ''Eliminate the US imperialist invaders.''
The balloon bomb, a fairly common way to send North Korean literature across the demilitarized zone (DMZ) into the South, is a reminder that although the two Koreas officially laid down arms nearly 30 years ago, a bitter war of words continues unabated.
Lee Wook Keun, president of the Seoul-based Naewoe Press, which monitors and interprets events in the North and refutes anti-South propaganda, said that the North Koreans had stepped up their attacks recently, perhaps to divert attention from their own succession problems.
South Koreans expect increasing border problems and propaganda attacks aimed at destabilizing the South now that Seoul has been chosen for the 1988 Olympics. According to Seoul government officials, the North has increased the number of loudspeakers along the 155-mile-long border from 12 to 94 in the past year; at least 70 of them are currently operating.
For an average of six and a half hours a day, the loudspeakers blast out praise for North Korea, President Kim Il Sung, and his son and appointed successor, Kim Chong Il. They denounce South Korean President Chun Doo Hwan and his government and call on South Korean soldiers massed along the DMZ to defect to the North.
South Korean officials are reticent about their own border activities. The Ministry of Defense refused, for security reasons, to give any information about loudspeakers on the south side of the border.
A US serviceman, however, said that sometimes loudspeakers were operating at the same time on both sides; ''I wouldn't think anyone can understand a word,'' he added. This may be the simplest way for the South to retaliate.
But loudspeakers and balloon bombs, though dramatic, have obvious limitations. Both sides rely primarily on radio broadcasts to get their message across the border and to the outside world. Seoul government sources say the North uses three main radio stations, two of them - Pyongyang Radio and Central Radio - official, and the third - the Voice of the Revolutionary Party for Reunification (VRPR) - clandestine.
The latter starts its daily broadcasts with the words, ''This is from Seoul, '' but technicians here have traced it to the North Korean city of Haeju.
The North Korean stations broadcast in several languages for between 11 and 23 1/2 hours per day, and are easily recognizable by their wildly emotive and hostile tone.
''No matter what trick he may use, traitor Chun Doo Hwan cannot conceal his dirty color as a splittist and a war maniac,'' commented the VRPR recently in Korean. And Pyongyang Radio translated an article from the official North Korean newspaper Rodong Sinmun into English, beginning ''The fascist, the murderer Chun Doo Hwan, having seized power by plunging thousands of, tens of thousands of, fellow countrymen into a sea of blood, has set up murderous torture chambers. . . .''
Americans are referred to as ''the arch foe,'' ''US imperialists,'' or ''aggressors,'' and the Japanese as ''reactionaries''; together they are accused of provoking a new war in the Korean Peninsula and of keeping South Korea as their colony.
South Korean officials, willing and even eager to give information about North Korean broadcasts, fall silent when asked about their own propaganda operations.
The Korean Broadcasting System (KBS), whose social education department is responsible for such programs, refused to be interviewed or to give any information on the grounds that ''it is not appropriate'' and ''we have not been given clearance.''
The KBS overseas section, Radio Korea, broadcasts news bulletins, commentaries, cultural and light-entertainment programs in several languages, showing South Korea through somewhat rose-tinted glasses and often with a strong anti-North Korea slant.
Another station, the ''Echo of Hope,'' though never mentioned by officials here, is believed to come from Seoul through KBS transmitters. North Koreans refer to it as a ''black'' or ''clandestine radio.'' Independent monitors here describe it as ''a carbon copy of North Korea's clandestine VRPR except that it doesn't use violent invective.''
Listeners say its propaganda is far more subtle; it features letters from Korean listeners overseas, historical and ideological lectures, and nostalgic popular folk music. Reunification of the peninsula along lines proposed by South Korea is a fundamental theme. Just how many of the thousands of words beamed across the DMZ daily actually reach the audience they are aimed at is difficult to assess. Seoul government sources think most broadcasts from the South are probably jammed in the North. One official said there was no jamming in the South, but the North's propaganda was so crude that its effect was minimal.
Other sources say it is difficult to pick up North Korean programs in certain areas, especially Seoul, because of deliberate interference. Korean author Peter Hyun, who visited China recently, found that Koreans there preferred the more subtle and varied KBS programs to the unadulterated political diatribe from North Korea.
Although some observers feel the bitter invective provides a safety valve for North Korean feelings, others worry that the tone is becoming more like a war cry and worry the words could lead to war.