One of the key topics in President Reagan's talks with Chinese leaders this week will be how to stabilize the Korean Peninsula. Spectacular and rapid results cannot be expected. But compared with the intractability of Middle Eastern or Central American problems, establishing peaceful, stable relations between Communist North Korea and US-supported South Korea seems at this time to be a more achievable goal.
North and South Korea continue to call each other names. But they have agreed to meet at Panmunjom to discuss forming a joint team for the Los Angeles and future Olympic events. The meeting scheduled for Thursday, the day of President Reagan's arrival in Peking, may be postponed until next week. An earlier meeting on the same subject broke up amid angry mutual recriminations.
China and South Korea, meanwhile, have improved relations visibly and substantially. South Korean athletes have competed in sporting events in China, and a Chinese basketball team recently played in Seoul. A Taiwanese team withdrew from Seoul in anger when the South Koreans permitted the Chinese to carry their five-starred national flag in opening day ceremonies.
''Our relations with South Korea have improved, but we have work to do with North Korea,'' a Chinese source commented recently.
Chinese Communist Party General Secretary Hu Yaobang is going to North Korea in May, soon after having seen President Reagan in Peking. Mr. Hu's visit this time is open and official, in contrast to his secret visit to Pyongyang with senior leader Deng Xiaoping a year ago.
Four great powers are vitally interested in the Korean Peninsula: the United States, Japan, China, and the Soviet Union.
Except for Washington, all are close neighbors of the two Koreas. Peace and stability in the peninsula, diplomats here agree, require first the agreement of the two Koreas and second the tacit or explicit support of all four powers involved in the region.
In the Korean war, US troops fought Chinese ''people's volunteers.'' Thirty years later, the atmosphere between China and the US is vastly different, as President Reagan's trip testifies.
But some things do not change. ''We have a land border with North Korea,'' said a Chinese who fought in that war. ''We do not have a land border with South Korea.'' Another Chinese source notes that China entered the Korean war for two reasons when American troops pushed toward the Yalu River.
''The first was to protect our own border. The second was to defend the socialist camp. Remember, at that time we were allied to the Soviet Union and felt we were part of the socialist (i.e., communist) camp as a whole.''
This source feels that while it was the Soviet Union that encouraged North Korea to start the war, it was only China that actually supported North Korea with ''people's volunteers.'' Moscow never became directly involved in the Korean war.
The lesson for China, this source says, is that never again should China get involved in a Korean conflict ''except to protect our own vital interests.''
There is a delicate inference here. At various times, notably immediately after Hanoi's conquest of South Vietnam in 1975, North Korea is believed to have tried to get China or Moscow or both to support it in a military invasion of South Korea. These efforts failed. But as long as Peking and Moscow were not on speaking terms, North Korea's Marshal Kim Il Sung could always try to play one off the other.
Today, however, Sino-Soviet relations are on a much more normal basis, even though Peking continues to stress the Soviet military threat to its security. Neither Peking nor Moscow wants a violent change in the status quo on the Korean Peninsula.
Peking will not openly accuse North Korea of bellicose intentions, but it has been quite categorical in asserting that it is opposed to all efforts to upset peace and stability on the Korean Peninsula, from whatever direction such efforts may come.
That was the formula used by Peking to express its scarcely concealed disapproval of the bombing that killed leading South Koreans in Rangoon, Burma, last October. Burmese authorities found unmistakable evidence of North Korean planning and execution.
Now Mr. Hu plans to go to North Korea after Reagan's visit here. Undoubtedly, he will use all his considerable persuasive powers to emphasize the advantages of the kind of economic open-door policy that China has been following in recent years.
Such a policy requires a peaceful international environment. There may be no immediate or visible results, but Washington, Moscow, Tokyo, and Seoul are all vitally interested in seeing whether Hu succeeds in moving Pyongyang one step out of international isolation and toward a more relaxed relationship with its neighbors.