In a move toward establishing the world's first communist dynasty, North Korean President Kim Il Sung's son was promoted today to a top position in the ruling Workers' Party. Kim Chong Il, the president's eldest son, was elevated to the number two position in the party, and ranked fourth among five members of the newly created standing committee of the party Politburo.

North Korea-watchers had widely predicted that the Workers' [Communist] Party would endorse Kim Chong Il 40, as heir apparent to his 68-year-old father. Senior North Korean officials recently hinted that the younger Kim would be promoted to secretary general of the party, but President Kim retained that post when appointments were announced at the close of the five-day congress held in Pyongyang.

But his appointment as number two in the party's secretariat, greeted with applause from 3,200 party representatives, was little less than ordaining Kim the younger as eventual successor to the leadership. He was also ranked fourth among 19 members of the Politburo and third -- after his father and the defense minister -- on the Central Committee's military affairs commission.

Kim Chong Il was born 40 years ago in the Soviet Union, at a time when his father was leading a guerilla struggle against Japanese occupation troops in Korea. He graduated from the Kim Il Sung University, where he studied politics and economics, in 1963, and received his first post in the Workers' Party in 1964. South Korean sources maintain that he was named successor to his father at a closed conference at the Workers Party in December, 1973, and has been de facto number two in the leadership since.

Because North Korea is closed to independent observers, and the doings of the leadership shrouded in thick fog, it has been hitherto impossible to accurately ascertain the younger Kim's standing.

It is incontestable that nepotism rules in this isolated country. President Kim's wife, Kim Song Ae, is chairman of the central committee of the Women's League, a female cousin is the vice chairman of the trade union federation, and the cousin's husband, Ho Dam, is deputy premier in charge of foreign affairs. Half a dozen other relatives and in-laws are known to occupy influential positions.

For South Korea, the elevation of the younger Kim, though anticipated, is a matter of concern. He is considered more doctrinaire and extreme than his father. South and North are bitterly antagonistic, divided roughly along the 38th Parallel since the war of 1950-1953. A peace treaty has never been signed.

According to South Korean roving ambassador Hahm Pyong Choon, the succession "is a source of great concern to us." Speaking in Tokyo last Thursday, the day before the congress opened in Pyongyang, Hahm said the younger Kim might attempt to unify the peninsula by force. "The son may fear for his power and try to prove himself by doing what his father has failed do -- unite Korea under communism," the South Korean diplomat warned.