Secretary of Defense Harold Brown will visit South Korea later this month to express U.S. concern about the fate of Korean opposition leader Kim Dae Jung, who has been sentenced to death by a military court, official sources said last night.

Brown will be the highest-level U.S. official to visit Seoul since the funeral last fall of President Park Chung Hee, whose assassination led to a political upheaval ending with a new period of military rule and neutralization of many former political figures.

The Carter administration has attempted through quiet diplomacy to convince the new Korean leader, President Chun Too Hwan, a former general, to commute Kim's death sentence. Brown's trip appears to represent a decision to give more public prominence both to the U.S. role in Korea and the Carter administration's pleas for Kim's life.

The United States maintains 40,000 troops in Korea, still one of the world's most sensitive trouble spots more than 27 years after the armistice ending the Korean War.

Sources said consideration is being given within the camp of President-elect Ronald Reagan to sending an emissary to Korea on a similar issue either before or shortly after Reagan's inauguration.