US reaffirms its 35-year ties to South Korea. Security, as always, is key topic for Reagan-Chun summit today

It will be a symbolic meeting of friends -- their third in four years. But as President Reagan greets South Korean President Chun Doo Hwan tomorrow, the occasion will be substantive as well as symbolic. Officials here say the summit will provide the chance to underscore the United States' commitment to South Korean security which began 35 years ago in June, with the onset of the Korean war.

Despite the bad press that attended the Chun government's clumsy reception for opposition leader Kim Dae Jung in February, administration officials say Mr. Chun's ``working visit'' comes at a significant time. It follows the freest election in South Korean history (Feb. 12) and the recent hints of a thaw between North and South Korea. It also comes as South Korea prepares to host several major international events, including the 1988 Summer Olympic Games.

For the most part discussions will focus on the perennial issues of security cooperation and the easing of tensions on the Korean peninsula.

In a meeting with reporters last week, South Korean Ambassador Byong Hion Lew described the military threat from North Korea as ``greater than at any time since the Korean war,'' citing evidence of major new troop deployments along the 30-mile-wide demilitarized zone separating North and South Korea.

Although State Department officials say there has been no qualitative change in the North Korean threat, they describe the nation's ``bristling military power'' and the bolstering of its frontline forces as ``worrisome.'' They say Mr. Reagan will be quick to reaffirm US support for South Korea.

As evidence of such support, Chun will be seeking increases or more favorable terms in the current $228 million US military aid package to South Korea. He will also look to the US to help stop the diversion of Western high technology to North Korea. The Chun government has charged that 87 US-built helicopters were recently smuggled into North Korea, apparently from West Germany. At a briefing for reporters yesterday, a State Department spokesman said the administration was ``extremely disturbed'' by the illegal sale, promising as-yet-unspecified ``countermeasures'' to ensure that the helicopters do ``not become a significant security threat to the South.''

Reagan and Chun are also expected to discuss prospects for a continuing North-South dialogue. Talks between the two Koreas began last fall on issues of trade and the reunification of families separated by the division of Korea. After a six-month hiatus, the talks are expected to resume in May. The Reagan administration is expected to encourage direct bilateral discussions, possibly with an eye to eventual four-power talks including the US and China.

The other major issue on the Reagan-Chun agenda is trade. Since the 1960s, export industries have given Korea one of the fastest sustained economic growth rates in the world. Trade with the US during this period soared from $200 million in 1962 to over $17 billion today.

At issue in the talks is a variety of tariff and nontariff trade barriers that have recently been erected in the US to restrict imports of Korean-made goods, including steel and textiles. The Koreans say these restrictions have begun to retard domestic economic growth. At the same time, some US products and services have been excluded from the Korean market. The Reagan-Chun summit will be used to reaffirm commitments to resist growing protectionist pressures that most agree pose the only real threat to an otherwise solid bilateral relationship.

The two leaders will also deal with the issue of human rights. The record of the Chun government has been the source of controversy since Chun consolidated power in the turbulent period following the assassination of South Korean President Park Chung Hee in 1979. Despite recent improvements, human rights activists say Chun still operates with an iron hand. A report last week by two New York-based human rights groups points to ``brutal tactics and extrajudicial methods,'' including restrictions on political and press freedoms and the forced induction of dissident students into the Korean Army.

Consistent with past practice, Reagan is not expected to make human rights a major issue, preferring instead, according to one State Department official, to ``give credit where it's due, while stressing there's more to be done.'' Sources here say the administration's reluctance to push too hard on human rights issues reflects a concern that too-rapid political liberalization could have adverse security implications in South Korea.

But US officials also say that quiet diplomacy has been effective, noting that recent gains -- including the release of political prisoners and February's elections -- have been ``impressive.''

``Korea's not a model of Jeffersonian democracy,'' says one State Department official, ``but they've come a long way.'' `Korea's not a model of Jeffersonian democracy,' says one State Department official, `but they've come a long way.'