A military courtmartial this morning sentenced to death seven of the eight men charged with plotting to assassinate South Korean president Park Chung Hee.

Lt. Gen. Kim Yong Sun, chief judge of the military tribunal, read out the sentences after pronouncing the seven men guilty of murder and attempted sedition.

The chief defendant, Kim Jae Kyu, had admitted shooting dead the president and his chief bodyguard at a dinner party in offices of the Korean Central Intelligence Agency on Oct. 26.

Kim, then director of the KCIA, had said he acted out of patriotic motives. But the prosecution said he shot Park with the wild hope of taking over the country through a revolutionary committee.

The death sentence also was ordered for Kim Kae Won, President Park's chief secretary who was present at the dinner and who was accused of failing to come to the president's assistance. He admitted that, but also said he had had known nothing of the plot in advance.

The five others given death sentences were KCIA aides who, it was charged, killed Park's bodyguards in places near the assassination room. All five claimed that they acted on Kim Jae Kyu's orders, and he had pleaded in court for mercy for them.

The eighth defendant, who had been accused of concealing evidence after the crime, was sentenced to three years in prison. The prosecution had demanded five years for him.

Kim Jae Kyu stood calmly and showed no emotion as the death sentence was read. He had said in a final court statement that he was ready to die.

The chief judge said those who assassinated Park "must compensate for the criminal act of treason against the state and nation."

He took note of Kim's claim that he acted to remove a dictator and to put the country on the road to democratic reform.But the judge said the court was not convinced that men who had been early supporters of Park's constitution "could have made such a sudden change."

The sentencing followed nine days of testimony that revealed no new major evidence in the assassination.

Today's verdict and sentences can be appealed both to an appellate court, where new evidence may be admitted, and to the Supreme Court. The one military officer involved can have his case reviewed by the martial law commander.

The death sentences ultimately will require the written approval of the defense minister because most of the country is under martial law.

Meanwhile, the South Korean government disclosed that President Carter had congratulated Acting President Choi Kyu Hah for his recent repeal of the emergency decree that had been used to jail many dissenters under Park.

Choi, who is to be inaugurated as Park's successor on Friday, repealed the "Emergency Decree No. 9" and freed more than 130 persons convicted under it in the past few years.

Carter also wished Choi success in realizing "the development of a broader political consensus in Korea."

Carter's letter, which received wide publicity in the morning newspapers here, appeared to be a public gesture of support for the civilian government at a time when its powers are threatened by a group of generals who overthrew the military establishment a week ago.

The president's letter was delivered yesterday by U.S. Ambassador William Gleysteen.

The government also revealed that Choi would announce a special amnesty for 1,646 other prisoners. The great majority of them are common criminals who traditionally are freed when a new president is inaugurated. But the number also includes some violators of two old emergency decrees who are still being held because they had violated other laws as well.

The latest amnesty means that virtually all of the political prisoners in South Korea are being released in the aftermath of Park's death despite wide authority exercised by military commanders. The exceptions are an undetermined number of persons accused of violating either national security or anticommunists laws, including the internationally known pet, Kim Che Hah.