Gen. Lee Hui Sung, 55-year-old infantry officer, emerged as South Korea's new military strongman today after a lightning intervention last night by a group of generals that left the future of the civilian government in doubt.

The military move yesterday resulted in the arrest of the martial-law commander, Gen. Chung Sung Wah, in a bloody clash that left many wounded, accordiing to reliable sources.

The recently elected president, ChoiKyu Hah, was not heard from publicly today. It was unclear whether the new military leadership intends to extend its power to the civilian sector.

Troops loyal to the new military leaders took command of key buildings in downtown Seoul. Rumors of a counterattack by the outsted generals' followers were widespread, but the city was quiet as the night curfew began.

The new generals imposed almost a total news blackout on their actions and took control of press censorship.

Last night's quick takeover -- initially explained as strictly the arrest of the martial law commander for a possible role in the Oct. 26 assassination of president Park Chung Hee -- is now described by informed sources as the result of a factional struggle between groups of generals. These sources also described the group now in control as "hard-liners" who were more loyal to the late president Park than the group that assumed martial law command after his assassination.

[Ambassador William Gleysteen met with South Korean officials to deliver a sharp U.S. warning, made public at the State Department in washington Thursday, against military intervention in the civilian government. wThere was no indication which officals he met, Associated Press reported.]

[In Washington, the State Department reiterated that disruption of movement toward a broadly based government in Seoul would have "a seriously adverse impact" on U.S. Korean relations. The statement referred to the latest changes as "realignments" and maintained that they did not appear to affect directly the civilian rule of President Choi.]

The new Korean strongman was promptly promoted to the rank of full general and appointed Army chief of staff, the position formerly held by Gen. Chung.

Ironically, Gen. Lee had been regarded as a protege of Gen. Chung, who had appointed him to the key position of director of the Korean Central Intelligence Agency shortly after Park was assassinated by the previous KCIA chief.

While the official reason given for Chung's arrest was that new facts had been obtained implicating him in the plot that resulted in Park's asassination in a KCIA dinning room, reliable sources familiar with the takeover advised reporters that was not the real reason.

There had been speculation, however, that Chung played a role in the slaying. He was near the scene on the fatal night and left it with the accused assassin, the then, KCIA director Kim Jae Kyu.

Speculation centered mainly on reports that the clique led by Gen. Lee was angry over alleged corruption within the military and over favoritism in promotions.

How big a role his clique's political view played in the takeover was the big mystery. Its members are said to have been more committed to president Park than other generals and they may have been irritated with the gradual move toward democratic freedoms that President Choi had embarked on. One source said the new leadership would favor a more gradual relaxation of the late president's stern rule.

Meanwhile, almost all important government business ground to a halt. The court-martial of Kim Jae Kyu and seven alleged accomplices was postponed and sources said Gen. Chung is also likely to stand trial.

President Choi, who disappeared from public sight, had been expected to announce his new Cabinet today, but a spokesman said that announcement had been postponed. A brief article in newspapers -- now censored by the new military chiefs -- said Choi approved of Gen. Chung's arrest, but that statement was not attributed directly to Choi.

An emergency meeting of the existing Cabinet left over from Park's rule, was held for the sole purpose of approving the promotion of Gen. Lee -- who had been a lieutenant general. It also confirmed his appointment as Army chief of staff.

The Cabinet meeting was presided over by Choi's new prime minister, Shin Hyon Hwack, an economic expert who had been deputy prime minister under Park.

It was primarily the absence of Choi that gave rise to speculation that the new crop of generals was dissatisfied with him and favored a harder line. Choi had promised to revise the constitution for direct election of the president and made special efforts to obtain the cooperation of opposition party and antigovernment dissidents, South Korea's latest period of unrest began Oct. 4 with the ouster of opposition leader Kim Young Sam from the National Assembly.

That move by Park's followers resulted in a sharp U.S. protest and mass resignation of the opposition delegates to the assembly. Student riots followed and the Oct. 26 assassination of Park heightened the instability that continues unabated.

The overnight military insurgency involved two clashes, the first at Chung's residence in this city of 8 million persons and the other at the Defense Ministry.

About 7 p.m., troops sent by Gen. Chun Too Hwan, defense security commander, surrounded Chung's home and tried to arrest him but were initially repelled by the martial law commander's personal bodyguard.

A gunbattle lasting nearly an hour ensued. It was described by Defense Minister Ro Jae Hyun today as a "minor" clash but sources said many were injured and taken to two nearby hospitals, which were sealed off to the public. Chung was arrested and taken away, reportly for interrogation in the Park assassination case.

It was rumored that one and possibly two officers had been slain, but there was no confirmation.

Combat jeeps with mounted automatic weapons were drawn up in the neighborhood, the area sealed off by troops and bridges over the nearby Han River blocked. All automobiles were ordered halted and thousands of persons streamed across the bridges on foot to reach their homes.

At about 2 a.m. a second clash occurred at the Defense Ministry. Its origins were not clear, but it is believed that some remnants of Chung's loyalist attempted to take the ministry away from Lee's insurgents.

The capital garrison forces, a special unit that provided security in downtown Seoul and been used by Chung after the assassination, was ordered to return to barracks. It was replaced by new forces, including paratroopers, assigned by the victorious generals.

A government statement issued this morning said that in addition to Chung a number of the other generals had been seized during the night for questioning in the assassination. The names were not disclosed, but sources said as many as ten top-ranking generals were under arrest. Besides Chung, those included Maj. Gen. Chung Byung Chu, a special forces unit commander, and Maj. Gen. Chung Tae. Hwan, who was commander of the division garrison in the capital.