A Southeast Asian foreign minister recently told me that "the big story of the past 30 years has been the East-West conflict, but the big story of the next 20 years is going to be the East-East conflict between Russia and China. That will affect every thing from now on."

With due allowance for hyperbole, there may be considerable truth in that prediction. The giants of the communist world are circling and being encircled by each other, like two heavyweight wrestlers, trying hammerlocks, footholds and feints. This geopolitical grappling has become much more intense in recent months, since China's sudden diplomatic activity worldwide and its accelerated drive for economic and even military-supply relationships with Europe, Japan and the United States.

To examine Soviet thinking behind the progaganda thrusts and counterthrusts, I had a long conversation a few days ago with a Soviet official who has extensive experience and significant responsibility in dealing with China. The major points he left me with were these:

First, China is considered to be far behind the Soviet Union in national power and thus a long-term danger rather than an immediate threat. Despite its size and reputation as a world power, it is "a very weak country," far weaker than Japan and even weaker than Italy. Even if all its ambitious industrial plans succeed, China in the year 2000 will approximate the Soviet industrial strength of 1970, according to the Soviet estimate.

It flows from this that major military action by China against Russia in the near future is unlikely, because "they rae not fools." Russia has strengthened its forces along the Chinese border, estimated by U.S. sources at one-third to one-fourth of Soviet military strength, but officials declare that the border is quiet and there is no Soviet intention to fight.

Second, the new Chinese drive, while motivated by the quest for internal development, utilizes anti-Sovietism as the basis for its appeal to the United States and other outside powers. "China's first task is to convince the West that it will not alter its policy toward the Soviet Union, so that the West will continue to help it build up its might," I was told.

Despite Peking's assurances, the suggestion here is that alliances with China are unreliable. Chinese ties with outside powers are seen as modern reflections of the age-old tactic of playing off one barbarian against another, and thus are inherently impermanent.

Third, the Soviets will not be angry or even worried if Washington establishes normal relations with Peking, which Moscow itself seeks over the long run. But the Russians react strongly against an anti-Soviet "China card" idea and any suggestion of aiding the Chinese military buildup.

There is suspicion here that Washington is behind the proposed China arms deals of Western European countries, which Moscow adamantly opposes. The recent China-Japan peace and friendship treaty, which the United States helped promote, worries Moscow because "it could be used as a bridge" to a militaristic Asian alliance on a racial basis.

Fourth, the recent Chinese diplomatic maneuvers in Eastern Europe are interpreted as aiming at splitting the communist camp, and Chinese flirtatiors with Iran and Turkey at "creating a hostile belly" for the Soviet Union. All of these are said to be unsuccessful.

There is much sharper concern here about Chinese activies in Southeast Asia, especially the growing conflict with Vietnam. Moscow is seeking to convince the West that China seeks domination over Asia to the jeopardy of Western as well as Soviet interests.

Though delivered in calm and confident tones, a Soviet analysis of the China problem also reveals a deep cultural and historic abyss. Even sophisticated Russian experts speak of Chinese as some Americans speak of Russians - driven by inexplicable motives to make trouble.

Throughout their history, the Russians have been concerned about the threat from the West and the possibility of a two-front battle for their vast continental country. This concern, at times, has caused some historic swings of their own in tactics and alliances.

Behind the propaganda level, the Soviets profess to be steady on course, with a watchful eye eastward but no need for precipitate action. As is the case in Washington, however, experts here may be more tolerant and cautious than political leaders. In any case, as the Asian foreign minister suggested, the Sino-Soviet conflict is a big, important story that bears careful watching.