The flare-up between China and Vietnam has intrigued most of the world as an ironic turn in the continuing Indochina war, which finally safeguards the rest of Southeast Asia against communist aggression. But here in Japan - which is in the midst of treaty negotiations with China - the rumble has been analyzed in the greatpower context.

The Japanese lean to the view that a continuing leadership strulle caused China to pick an unnecessary fight with Vietnam. As a result, the Chinese have completed their own encirclement and handed yet another international gain to Moscow.

As the Japanese see it, the Chinese leadership struggle pits a faction lining up behind Party Chairman and Premier Hua Kuo-feng against another faction behind Vice Premier Geng Hsiao-ping Chairman Hua is the hand-picked successor of Mao Tse-tung and is thus glued to Mao's intense hostility to Russia.

Vice Premier Teng is committed to the modernization of China's industry, agriculture and military forces. He needs an external enemy to mobilize the country, and since Japan and the West are the most likely source of new technology, he too, is wedded to the anti-Soviet line.

The upshot is an internal competition as to which faction can be most beastly to the Russians. The Chinese thus approach the rest of the world as a kind of Manichaean power. They insist that all other countries be for them and against the Russians.

The tension with Vietnam is a striking example. The Vietnamese have long tried to hand midway between Russia and China, the better to get aid from both communist powers in their continuing effort to take over Laos and Cambodia and thus dominate a unified Indochina. But the Chinese, demanding a more anti-Soviet attitude, have helped Cambodia resist Vietnam.

Hanoi has responded by forcing resident Chinese out of Vietnam, and leaning toward Moscow. So besides having a hostile communist superpower on its northern flank. China now has a hostile minipower on its southern flank.

The Japanese see the same pattern in their negotiations with Peking for a treaty formally ending World War II, negotiations that have been going on since the normalization of relations between the two countries in 1972. As one feature of the treaty, the Chinese have insisted on a clause condemning any country seeking world or regional hegemony. The clause was obviously directed against Russia, and the Soviets put pressure on Japan not to sign. The Japanese, unable to elicit softer language from Peking, and unwilling to antagonize Moscow, shelved the project.

In April of this year, a fleet of over 120 Chinese fishing boats suddenly surrounded the Senkaku Islands, which Japan occupies and China claims. The government of Prime Minister Takeo Fukuda reacted adversely, and Peking withdrew the boats saying the incident was an "accident."

But since the boats came from several different ports, the "accident" theory is dismissed here. Rather, the view is that the Chinese, working against the background of their internal struggle, were putting crude pressure on Japan to sign the treaty complete with anti-hegemony clause. Mr. Fukuda, when he came to Washington early in May, was more than ever determined not to accept China's terms.

From May 20 to May 23, President Carter's national security adviser, Zbigniew Brzezinski, visited China. The Chinese expressed to him their interest in concluding the treaty with Japan. On May 23, Brzeinski met with Fukuda. On May 26, Japan asked China to resume the treaty negotiations.

But even though the United States favors the treaty, and though the treaty is popular here as a way to wipe out the last stain of Japanese war guilt, Fukuda has been extremely cautious in approaching the Chinese. When Peking postponed negotiations, he also postponed. Now the talks, orginally scheduled to begin yesterday, will not begin until July 21. Moreover, Fukuda continues to insist that he will sign only if the Chinese soften the anti-Soviet language.

Japan's prudent approach, I think, serves as a useful model for the United States. While Washington ought to have good relations with Peking as part of its strategy for dealing with Moscow, the Chinese and their divided leader ship are really not a good card to play against the Russians. On the contrary, the basic trick is to move simultaneously toward better relations with both communist powers.