The U.S. and Japanese governments expressed deep concern yesterday over the death sentence imposed on South Korean dissident leader Kim Dae Jung.

Kim, 54, was convicted earlier in the day by a military court in Seoul of plotting rebellion and sentenced to death by a panel of four generals and a lieutenant colonel. Both the United States and Japan, South Korea's closest allies, earlier had indicated that if Kim were executed, relations would be adversely affected.

Secretary of State Edmund S. Muskie, recalling the "deep concern" expressed in the past, labeled the verdict "extreme." He added: "Nevertheless, since the case is subject to judicial review and since the government of the Republic of Korea is fully aware of our views, we will have no additional comment on the matter at this time."

U.S. officials have indicated confidence that the outcome of the review process will be commutation of the death sentence. The process outlined in Seoul could take about two months.

President Chun Doo Hwan could save Kim's life even if the appeal process under the military court failed to do so. Rep. Lester Wolff (D-N.Y.) of the House Foreign Relations Committee said, "I and many Americans appeal to President Chun for compassion."

In Tokyo, Japan's vice foreign minister summoned the South Korean ambassador to express official concern, according to ministry officials. They said, however, that Vice Foreign Minister Masuo Takashima had not suggested a reduction in the sentence because that would have constituted interference in South Korea's internal affairs.

Japanese Foreign Minister Masayoshi Ito told reporters the sentence had been more severe than expected in Tokyo.

Foreign Ministry sources said South Korean Ambassador Choi Kyung Rok said Seoul hoped Japan would not make a great fuss about the case so that "things could be handled more easily."

The Australian government deplored the sentence and Foreign Minister Andrew Peacock told Parliament in Canberra that Australia's warm ties with Seoul "could be eroded if the sentence is carried out."

In Bonn, Foreign Minister Hans-Dietrich Genscher called on West Germany's European Community partners to join his government in demanding that Kim not be executed.

The International Commission of Jurists described Kim's trial as "a mockery of the process of demmocratization that the South Korean government claims to be pursuing," and asked Chun to commute the death sentence.

The Geneva-based commission, an independent body of distinguished lawyers, deplored the absence of qualified legal observers at the trail, the arrest of three chosen defense lawyers, and severe limitations imposed on the calling of defense witnesses.

Japan's biggest labor organization, the 4.6 million-strong General Council of Trade Unions decided to hold regional protest rallies and started a drive to collect 10 million signatures to back an appeal to South Korea not to execute Kim.

Even though South Korea is protected by 40,000 American servicemen and receives considerable U.S. aid and trade, President Chun had indicated little concern over what the Carter administration has said about Kim.

The verdict is to be reviewed within 10 days by the martial-law commander, then sent automatically to a higher military court and the nation's Supreme Court. Chun, the man who ordered Kim's arrest and prosectuion while a lieutenant general and military strongman last May, will have the final review, and a chance to commute the death sentence.

In the month-long trial, the martial-law authorities accused Kim of plotting rebellion in connection with student-led antigovernment demonstrations in Seoul and the bloody protest in Kwangju last May, and with violating the national security act, the anti-communist act, martial law and decrees banning political activity, and the foreign exchange control act.