N. Korea: no promotion for Kim's son, but he is still heir

North Korea, often labeled ''the most secret society in the world,'' continues to baffle political analysts and prove their most confident forecasts wrong.

The succession, or ''Kim dynasty,'' issue remains a matter of intense speculation. Last month most ''Pyongyang-watchers,'' the South Korean government included, professed surprise when Kim Jong-Il, the son of North Korean President Kim Il-Sung, was not elected one of the nation's three vice-presidents.

Kim Il-Sung has ruled the Democratic People's Republic of Korea since it was founded in 1948. He has become the object of an extraordinary personality cult; his political philosophy, called juche (meaning self-reliance) is given the credit for virtually all progress. But observers point out that an estimated debt of $2 billion to foreign creditors shows that outside help has also been welcomed.

Last month, President Kim, whom North Koreans call ''the respected and great leader, the beloved father,'' celebrated his 70th birthday. Although there were strong indications that he intends to stay in power, observers in Seoul and Tokyo say President Kim has been working for many years toward eventual handover of power to his son.

But some analysts say the concept of a communist dynasty causes embarrassment to North Korea's main allies, China and the Soviet Union. It also appears to have met with some resistance at home.

The younger Kim is said to be in charge of much of his father's day-to-day business. He also holds the second most important post after Kim Il-Sung in the ruling Korea Workers' (Communist) Party. But he has never held a government post , and a vice-presidency was expected to give him government experience and international stature.

The fact that he was not elected is generally thought to be because of opposition to the Kim dynasty within the military, especially among the older Army officers. As further evidence of this, experts on North Korean affairs point to comments reportedly made by President Kim at the end of last month, emphasizing that the Army is subservient to the leadership of the party - that is, himself and his son.

In spite of these apparent setbacks, there have been firm indications that the acceptance of Kim Jong-Il as his father's political heir is still the official line. A senior Japanese trade unionist confirmed this after a 90-minute meeting with President Kim in April.

The KCNA - North Korea's official mouthpiece - has used increasingly laudatory language when referring to Kim Junior. This month it reprinted an article from a Hungarian weekly, which said ''Comrade Kim Jong-Il is the successor to the revolutionary cause of President Kim Il-Sung'' and ''the people of this country (North Korea) shout for joy simply at his august name.''

South Korean sources, however, say the ''joy'' is not as widespread among North Koreans as the official line would have the world believe. Two North Koreans who defected to the South claim that about 105,000 North Koreans are being held in eight concentration camps as ''ideological criminals'' under the direction of Kim Jong-Il.

The two defectors, both said to have been with the North Korean Ministry of National Political Security, told reporters in Seoul recently that more concentration camps, called ''special control areas'' were being set up in remote mountainous regions ''to isolate the ever-increasing antiparty elements disloyal to the clan-rule system in the North.''

Although Kim Il-Sung has been South Korea's archenemy for three decades, many people in the South fear that the younger Kim, still very much an unknown entity , might prove to be even more ''gung-ho'' than his father, if only to build up his own hero image at home.

Analysts here take some comfort from the fact that neither China, with its fledgling friendship with the United States, nor the Soviet Union, already hard-pressed by its own military and economic problems, is likely to welcome increased hostilities or tension on the Korean peninsula.

Some expect them to disapprove of a Kim dynasty, which clearly runs contrary to basic communist ideals. But according to officials here, neither of the North's powerful allies has made any public comment on the matter so far.