South Korea's loss of so many of its highest officials in the Rangoon terrorist explosion cannot help but heighten tension among South Koreans and their government.
Still, Mr. Reagan's planned visit shortly takes on greater significance. The overriding goals of ensuring Western security links and leading South Korea toward democratic rule must be pressed even more as guideposts of Western policy in the region.
South Koreans, with a reputation as a volatile people, have been having trouble enough evolving their own form of democracy from strong-man rule. The downing of South Korean Airlines Flight 7 by the Soviets in August had sent one jolt of anguish through the public and the government leadership.
Particularly distressing is that so many men of such high caliber, at least 19, were killed. The immediate worry is that President Chun Doo Hwan will turn to his Army cronies for less qualified talent, instead of reaching out to a broader spectrum of South Korean talent - which he must do eventually to prepare for the transition to less authoritarian rule he has promised for 1988.
President Reagan should keep Seoul on his itinerary for next month. He will openly affirm the security bond between South Korea and the United States. After all, a four-star US general presides over the South Korean military force, under United Nations rules. Even more to the point, South Korea considers the US about its only friend in the region. It needs reassurance against historically its biggest fear - US withdrawal, leaving the region to a reawakened Japanese overlordship. Korean memory of life as a Japanese colony remains vivid.
Principally for security reasons, plus the turmoil following the assassination of President Marcos's rival, Benigno S. Aquino, in Manila, Mr. Reagan has already canceled the Philippine, Indonesian, and Thailand segments of his November tour. Some analysts maintain he should have kept his Manila date, to pressure Marcos and reassure him toward a moderate political succession. Such a delicate dual role is vital in South Korean relations, too.
President Reagan behind the scenes should encourage Chun to permit freedom of the press and other democratic rights, to allow those dissatisfied with Chun's regime to avoid having to take the street to express their dissent.
South Korea is in the midst of deep change. Prosperity and industrialization are altering the country. One-fifth of all 40 million South Koreans now live in Seoul - 8 million in all, making it one of the world's major cities.
At the same time, South Koreans feel uniquely isolated, more so than the Japanese. Geography has placed South Korea at the end of the defense line from the West - with North Korea, China, the Soviet Union, threatening above it. Ironically as well as tragically, the major government mission aborted last weekend after the Burmese shrine explosion was to have continued to India, Sri Lanka, Australia, New Zealand, and Brunei. The purpose of the high-ranking trip was to carry over into political life the spread of South Korea's economic ties in the region. This was a significant outreach mission.
Mr. Reagan and Mr. Chun have some economic issues to sort through. The US would like more access to Korean markets, for products like computers and services like banking. The South Koreans want to sell the US more shoes and textiles.
But the bigger issue is the evolution of South Korea, a Confucian society, into a democracy. The problem of Korean unity is beyond reach for as far as analysts can see ahead. North Korea seems about to become the first Marxist state to practice dynasticism, that is, to pass government rule on to the present ruler's son. The two contrasting Korean systems appear beyond compromise.
For a Chun, permitting an opposition to take root is difficult in a way not perhaps readily visible to non-Asians. In a Confucian society, where the state is accorded something akin to sanctity, there is no room for an opposition party. There is no tradition of ''loyal opposition.'' South Korea is a contemporary Confucian culture with strong authoritarian overtones but some engagement with Western democracy. It remains a garrison state, obsessed with the threat from the north.
The Japanese have developed their own unique form of democracy in that part of the world. Mr. Reagan should encourage the South Koreans to do the same.