HE IS PUDGY, with a bland, moonlike face that rises unportentously from the dard military-style tunic affected by the North Korean leadership. He is the second most powerful man in North Korea.

He is a central figure in an elaborate, quest-mystical cult that is being contrived myth by myth in what amounts to a rewriting of the last 80 or 90 years of Korean history. Yet his name is never mentioned in the North Korean media.

Now about 37 or 38, since his mid-20s he has held a succession of key posts, usually ones that put him in a position to insure that there would be no challenge to the power and authority of President Kim Il Sung.

He is Kim Jong Il, eldest son of President Kim Il Sung and Marxism's first crown price. To the ill-concealed dismay of other socialists states, particularly the Soviet Union, the world is witnessing the creation of a new Asian dynasty in the Stalinist atmosphere of Pyongyang.

"If you don't understand the succession issue, you don't uderstand North Korea," is the way one analyst sums it up.

Though foreigners visiting North Korea have seen pictures of Kim Jong Il standing beside his father, the country's media never refer to him directly. He is called such things as "the party center," or, in frequent rhetorical flights of fancy, "the rays of the sun."

Recently, the North Korean people have been exhorted to see that the precepts of their "wise and beloved Leader" continue on "from generation to generation." Certainly the succession of Kim Jong Il will assure this. A Growing Pantheon

THE CULT of Kim II Sung has always been overwhelming. Prof. Young C. Kim of George Washington University, who has visited North Korea twice, says, "The intensity and frequency of hyperbole employed in praising the Leader is beyond description."

Nevertheless, since the early 1970s, or about the time that Kim Jong Il was first being brought close to the seats of power, the cult has taken on a new dimension.

It has been found, for instance, that the president's father, Kim Hyong Jik, a rural practitioner of traditional medicine, had been a revolutionary plotter against Japan's colonial rule.

In March 1975, Kim Jong Il's mother (the presidents first wife), Kim Jung Sook, was raised to the pantheon. A statue of her was unveiled in Pyongyang and she was hailed as an "indominable Communist revolutionary fighter" who "fought for the sake of the Great Leader, sacrificing her youth and life" in the war against the Japanese. The eulogy went on to tell how she had washed the Leader's socks and dried them in her bosom "and sometimes she cut her hair to spread it in the Leader's shoes."

There is more, much more, to the growing legend but there seems to be one principal objective: to show that the "roots of the dynasty are legitimate and run deep."

One side effect of the cult is to give the impression that Kim Jong Il was born on Korean soil. But western analysts think the truth is that he was born in the Soviet Union when his father was there receiving political and military training during World War II. In North Korea's present atmosphere of fervid nationalism, foreign birth would be an almost fatal political handicap. The Rise to the Top

KIM JONG IL is believed to have begun his political career as personal secretary to his father. He was shortly moved over to the Communist Party's important Department of Organization and Guidance. In 1972, he was named party secretary in charge of propaganda and organizational control, and at this point it become obvious that he was being groomed to succeed his father. In 1974, Kim Jong Il was apparently given authority over North Korea's relations with the South and Japan.

In his rapid rise to the top, Kim Jong Il eclipsed his uncle, Kim Yong Chu, the president's younger brother and the man most analysts thought was the designated successor. Yong Chu is said to have been found wanting because of his age, incendiary temper and lack of mental agility.

Kim Jong Il had been identified with what has become Pyongyang's particular contribution to Communist political practice, the so-called Three Revolutions Teams. These appear to be flying squads of party officials and technical experts sent from Pyongyang to serve as troubleshooters in factories and communes throughout the country.

Because officials in outlying areas had fallen into the old, inefficient and arrogant ways of the mandarins, the teams were created to serve a real need. From the extensive defense of their role carried in the party press, however, it seems obvious that they are deeply resented as interlopers. They can serve as a channel for Kim Il Sung's control of the smallest detail and a device to thwart any opposition from developing in the countryside.

As is inevitable with those who live in the shadows, Kim Jong Il is the subject of many rumours, most of them of dubious authenticity. A particularly lurid one surfaced earlier this year in the Korean community in Japan and has won wide acceptance.

Last fall, the story goes, Kim Jong Il was the target of an assassination attempt by young officers loyal to a prominent general who had just been purged. Kim Jong Il was reportedly run over by a car and lay in a coma for several weeks. Early this year, the story goes on, a prominent Japanese physician was approached by a North Korean agent. The agent said that his government was seeking the doctor's help in treating the son of a leading Pyongyang official who was suffering from a severe head injury. The injured man was said to be in his mid-30s.

Informed sources in Washington say there apparently was such an approach made to a Japanese doctor but that the patient involved was not Kim Jong Il.

There is a consensus that Kim Il Sung is facing considerable domestic opposition in having his son anointed as his successor. The evidence is largely circumstantial, consisting of such things as the ceaselee defense of programs identified with Kim Jong Il and the failure to convene a Korean Workers' (Communist) Party Congress, now more than a year overdue.

Analysts discount reports that poor health is forcing Kim Il Sung to settle the succession question as soon as possible. From time to time there are stories that Kim has flown off to an Eastern European country for treatment of some serious illness. Kim has a large growth on the right side of his neck that, the rumors say, is malignant. Analysts doubt that and say that as far as they can determine Kim Il Sung is in robust health for a man of 66, still able to maintain a gruelling pace, albeit with occassional periods of prolonged rest. The Roots of the Cult

THE NEAR-IDOLATRY surrounding Kim Il Sung has many points in common with other leadership cults of recent times such as Stalin's and Mao's. Among them:

It had its roots in a society traditionally accustomed to strong, if not absolute, rule from the center.

The cult appears to be the natural result of the leader adopting a seemingly irrational and dangerous policy - in the case of North Korea, a policy that antagonizes powerful foes and natural allies at the same time. It seems almost axiomatic that the greater the risk, the more elaborate is the cult.

The cult confers at least a vensor of legitimacy on the leader's somewhat shaky claims to ruin. In the case of Kim Il Sung there were at least a dozen other personalities with more substantial nationalistic credentials when he arrived in Pyongyang after World War II as a major in the Soviet Army. It took him almost a decade to remove all his important rivals.

The cult develops a degree of social cohesiveness among the people. It is no accident that leadership cults are invariably wedded closely to the country's most heroic and inspirational legends.

The cult enables the leader to be more politically flexible than any faceless, anonymous committee could be.

The cult of Kim Il Sung began its greatest development in the late 1950s when he was being whipsawed by the mounting quarrel between North Korea's great patrons, the Soviet Union and China. The Soviet and spigot was being turned off to pressure Pyongyang to take sides at a time when the country was still painfully rebuilding from the devastation of the Korean War. Presumably, Kim felt that to choose between the two rivals would create even greater problems. At the same time, North Korea's priorities - withdrawal of U.S. troops from South Korea, economic development and unification of the peninsula - were not necessarily those of Moscow and Peking.

Kim opted out. He symbolically threw up a wall around North Korea's borders and turned the country in on itself. The nation's goal - and its ralying cry - became juche, the translation of which has overtones of both self-reliance an self-identity.

Juche would bring prosperity; juche would bring pride; juche would unlock the energy and creativity of the Korean people.

Juche would also free Kim II Sung to pursue an aggressive, probing policy toward South Korea at a time when China and Soviet Union were becoming more interested in relaxing tension in that particular corner of Asia.

By the standards important to Pyongyang, juche was an impressive success - at least in the short run. For a decade or more, the North developed an economy that far outstripped South Korea's and a military machine that, in many respects, still surpasses Seoul's.

In 1965, the gross national product in the North worked out to $375 per person as compared with $245 in the South, but, in recent years, Seoul has turned the situation around. According to 1976 figures, South Korea had a gross national product more than twice that of the North's, $21.6 billion to $10 billion, and per capita GNP in the South edged ahead of the North for the first time $605 to $590. And a study prepared earlier this year by the Central Intelligence Agency predicts that the South's GNP will grow to $34 billion in 1981, while the North's rises to only $13 billion.

The cult of an infallible Kim II Sung and the emerging myth of the dynasty come across to the outside world as often bizarre, frequently fatuous and generally irrelevant. Certainly ridicule seems the only proper response to reports that egg production has increased following what amounts to a state visit to the roosts by "the great and beloved Leader." Cadre seeking policy guidance may be forced to look for it in vague poetry.

Yet the Kim Il Sung cult cannot be dismissed as a simple aberration, a mere figment of Pyongyang's propaganda apparatus. Prof. Kim of George Washington University came away from his visits to North Korea surprised at the sincerity he detected among individuals who spoke of their respect for Kim Il Sung. Even allowing for the fact that most of the people he met were middle-level officials with a stake in the system, Prof. Kim was impressed.