The clique of generals now ruling South Korea represent a new type of nationalistic officer imbued with a sense of mission and convinced that they also can guide the nation's politial and economic life.

Four of them form the core of the new regime which rose to power out of the turmoil that followed President Park Chung Hee's assassination last October. As soldiers, they have rejected South Korea's fledgling democratic institutions in favor of direct military rule. As nationalists, they have spurned American advice not to do that.

The new ruling elite seems to be defined by collective absence of clear political philosophy, lack of understanding of domestic politics, and a vague nationalist impulse to seek "Korean solutions" to Korean problems.

The four top generals are Chon Doo Hwan, acting director of the Korean Central Intelligence Agency and the chief of the military intelligence; Ro Tae Woo commander of the Seoul garrison; Chung Ho Yung, comander of the Korean Special Forces; and Kim Bok Dong, chief of staff of the 3rd Army which is stationed around the capital.

The first three are members of the committee announced this morning that is at the pinnacle or power.

All four were born at Taegu, in North Kyungsang Province, and except for Chun all attended the same high school. But the close group was apparently formed when all four attended the same class of the Korean Military Academy. Since their graudation in 1955, they formed a clique within the officer corps.

Another aspect of their common experience contributed to their sense of mission. The class of '55 was the first requiring four full years of training. In contrast to their hastily trained senior officers who rose in the ranks by virtue of experience in the Korean War, the four regard themselves as the first true professionals. All have served in the Vietnam war.

Clearly their leader now is Chon, 48, a protege of the late president Park and eventually deputy chief of the presidential security force. He was not a senior general before the military mutiny last December.

For several weeks after the four staged the Dec. 12 intra-military coup and arrested the Army chief of staff, they operated as a group and outsiders believed they formed a kind of collective leadership in which all were equal.

But the tall, bald Chon recently has emerged as preeminent, or as one Asian diplomat put it, "a bit more equal than the others."

Chon stepped out front by assuming authority to deal with many civilian groups and by taking responsibility for shaping the new government council that will rule the country for an indefinite period.

Those who have dealt with Chon describe him as a man of total self-confidence in his ability to decide what's good for South Korea. "He thinks he was born to wear the purple," is how he is described by one person who has conferred with him many times on political and military matters.

Chon and his colleagues were known within the Army as strong nationalists and devoted admirers of Park and one of their first decrees after the May 17 bloodless coup bans any slurs on the late president's name.

They were resentful of what they believed was corruption and favoritism in high military circles around Park and felt that their own careers were being blocked by the elder generals who refused to retire. "They felt they were visitors in the house that they really should own," said one source.

Their indifference to American influence was first visible on the night of Dec. 12 when, to prevent a counter-coup, they broke a long-standing agreement that troops under the joint U.S.-Korean command could not be moved without approval from the U.S. Commander, who is Gen. John A. Wickham.

Since then they have routinely ignored American officials' advice that a further accretion of military power might force the Carter administration to reevaluate its commitment here. When Chon took command of the powerful KCIA, the U.S. Embassy was informed at the last minute.

When asked at a news conference about reports of U.S. irritation at that appointment, Chon said it should be no concern of the Americans who was appointed.

There was only brief advance notice to the Americans when they assumed total control on May 17 and began arresting many political and dissident leaders.

Throughout all these events, several sources say, the generals coolly calculated that the United States would not retaliate by threatening to withdraw more of the 39,000 American troops stationed here.

They are described as feeling that the American troops will remain indefinitely because it is in the American interest to keep them here, not for any altruistic reasons of defending this country from North Korean attacks.

Their distrust of civilian politicians is not unique with them but is widely shared in the South Korean military sources have said. Even before the latest crackdown, they had let it be known that none of the three potential candidates was acceptable. They also spread the word that political debate, which grew lively with the promise of elections, was divisive and harmful to national unity.