President Park Chung Hee was assassinated in a plot organized by the South Korean Central Intelligence Agency director and involving at least five members of the director's staff, the government announced today.

Reversing an earlier claim that Park had been killed in an accident, the government said he was deliberately killed by KCIA Director Kim Jae Kyu, who had first shot the president's chief bodyguard, who was also a close aide.

Kim and the five were arrested and a government spokesman said that "many other [KCIA] personnel" are under investigation. Kim gunned down the bodyguard and Park inside a KCIA dining room, and his associates shot to death four of Park's other bodyguards and wounded another almost simultaneously, the government spokesman said.

He said Kim acted because he knew Park distrusted him and because of fierce anger against the chief bodyguard, who blocked many of his recommendations before they could reach Park.

The new account differed radically from earlier stories put out by the government after the killings Friday night. The government's first announcement Saturday morning said only that Park had been "incapacitated." Later it stated that Park was killed accidentally when a quarrel broke out between Kim and the chief bodyguard.

Today's announcement came as an "interim report" on the slayings released by a joint investigative command under supervision of the martial law authority. Martial law was imposed yesterday throughout almost all of the country of 37 million.

Despite apparent calm, close to 12,000 troops were posted throughout the capital, the usual midnight to 4 a.m. curfew was expanded to 10 p.m. to 4 a.m., unauthorized public gatherings were prohibited and the news media were under military censorship.

The "tragedy" of the slaying was caused, said chief investigator Maj. Gen.

Chun Du Whan, "by the secretly planned criminal acts of Kim Jae Kyu," who organized the plot, apparently on Friday afternoon, after being informed that Park wanted to see him that night. He said Kim feared he would be dismissed in a rumored shakeup of government posts.

In saying that "many others" were being investigated, the report implied that a widespread KCIA plot was behind the killings, but no details of the involvement of others were given.

Meanwhile, thousands of South Koreans lined up today at public altars set up in the capital and throughout the nation to pray and burn incense for the late president.

Opposition leader Kim Young Sam joined Acting President Choi Kyu Huh, who had been Park's prime minister, and other government officials in paying last respects to Park, whose body was lying in state at the official Blue House residence.

And Kim Dae Jung, a leading critic of Park's authoritarian rule, warned North Korea not to take advantage of any possible leadership vacuum.

I warn North Korea not to take advantage of the current situation as the entire people's voice is united [against communists], transcending political differences," he said in a statement read by a Seoul radio station.

"We must avoid any internal confusion. However, the current difficulties can be solved only through restoration of a democratic system," he said. Kim Dae Jung had been imprisoned by Park for three years and remained under house arrest after his realease last December.

Chun's account today noted that KCIA chief Kim "had been distrusted by the president in his handling of business." This, however, did not answer the question of why the president and his once-trusted aide that falled out.

There is speculation here that both Park and his now-dead chief bodyguard, Cha Ji Chul, had wanted Kim to crack down harder on student demonstrations and political opponents.

Kim had been accused several times of incompetence in carrying out his duties by Park and feared dismissal when he was summoned by Cha to dine with Park at the KCLA compound near the presidential mansion, the interim report said.

This is the detailed account of events Friday evening provided today in the interim report:

Park, his chief secretary, chief body guard Cha, and Kcia'' chief Kim sat down to eat at 6:20 p.m. Kim and Cha began arguing. Kim left the room 30 minutes later and, as he had "preplanned," gave this order to two aides:

"When you hear shooting inside the rom do as you are told."

Then he went to an upstairs office, got a pistol, and returned to the dining room where Cha repeated some accusations against him.

At 7:30 p.m., Kim emerged from the room and confirmed that his men were ready. He returned to the dining room and called Cha a nasty name. He fired one shot at Cha and then shot Park. Then he shot both again.

Outside the dining room, his five aides -- two bodyguards, a driver, a secretary and a protocol officer -- went into action as two teams. One team killed three of Park's bodyguards in a nearby kitchen and the other team killed two more guards at a nearby, indisclosed location.

Kim used a .38-caliber pistol and four of his aides had identical weapons. The fifth aide used an M16 automatic rifle to make sure the bodyguards were dead.

The government report was vague on what happened after the shootings.

There was no explanation of why the KCIA's Kim did not also kill the fourth man in the dining room, Park's chief secretary, who is a former director of the KCIA.

It said that that secretary, Kim Kye Won, made a report on the shootings to "martial law headquarters" but the time at which he did that was not given. Martial law was not imposed on Seoul until 4 a.m. Saturday, about nine hours after the slayings.

It was after Kim Kye Won's report that martial law authorities arrested the KCIA's Kim and the five others and ordered an investigation of "many other personnel."

In the government's first report, issued on Saturday, the secretary Kim had been the one who had driven Park to the hospital, where he was pronounced dead at 7:55 p.m. Friday. That point was not discussed in the report issued today.

It was not clear how long in advance Kim had planned the killings, but the wording of the government statement implied that it was hastily contrived. Kim was told that Park was coming to dinner about 4:30 p.m. that afternoon, less than two hours before it began. It suggests that he plotted the shootings sometime in the period with his associates.

The government apparently issued the interim report to quell speculation and answer some of the main questions left unanswered in its earlier accounts.

The main question had been how Kim could have gunned down so many people alone and escaped alive. The new announcement today also raised to five the number of bodyguards killed along with Park. The figure had been either three or four before.

South Korea's constitution provides that a new president must be chosen within 90 days by the National Conference of Unification, a body of about 2,500 people from all walks of life. Most have been supporters of Park.

The U.S. military commander in South Korea, Gen. John A. Wickham, met top South Korean defense officials today to reiterate American support.

He said later that joint U.S.-South Korean forces were "adequate to meet any possible requirements that may develop" and that the United States was "prepared to defend the Republic of Korea under any circumstances."