North Korea issued today what appeared to be an official rejection of the American and South Korean proposal for tripartite talks on eventual reunification of the Korean peninsula.

At statement of the North Korean Central News Agency, monitored here, denounced the proposal. It quoted a Foreign Ministry official in Pyongyang as saying the idea is "utterly infeasible."

The proposal for three way talks was the highlight of President Carter's summit talks with South Korean President Park Chung Hee. Released July 1 in an official communique marking the end of the visit, the proposal represented a concession on the part of the South Korean government, which has been cool to the idea of three-way talks.

The proposal suggested that talks leading to eventual reunification of the two Koreas should begin with senior representatives from each of the three countries.

Previous comments from Pyongyang had indicated the North Korean government was cool to the idea but today's statement was the first formal rejection.

The statement asserted that the United States has no business getting involved in reunification, which the North Korean government contends is a matter to be discussed only between it and South Korea.

"Why should the United States get involved in the dialogue between the Koreans for the solution of the question of the Korean unification?" the statement asked according to Kyodo News Agency, which monitored the Pyongyang broadcast.

U.S. involvement, it said, would be "an interference in our internal affairs."

North Korea insisted it should talk separately with the United States but only on the subject of the withdrawal of the American troops from the South and on replacing the 1953 armistace agreement with a formal peace treaty.

The statement said that South Korea would be permitted to participate in those talks only as an observer.

The statement also reinterated the North Korean formula for opening reunification talks with the South, calling for a "dialogue" that would include not only official representatives but also members of various political parties and social groups.

In the past, South Korea has insisted that the reunification talks should include only official representatives of the two governments. It regards the proposal to include representatives of political parties and social groups as an effort to divide the South.

The U.S.-South Korean proposal was designed initially as an effort merely to reduce tension on the peninsula but eventually, it was hoped, the talks would be expanded to include steps toward reunification.

The message was transmitted to Pyongyang on July 1 by a third country, which reportedly was Indonesia.

American sources had said that North Korea's two principal Communist patrons, China and the Soviet Union, were being asked to use their influence in Pyongyang to bring about the talks.