A Far Eastern visit concentrates one's mind on developments there. Though several Asian countries are disquieted by recent events, the focal point of foreboding is the Cambodia (Kampuchea)-Thailand border, where Vietnemese troops are now accumulating. Were those troops to move into Thailand, America would face some excruciating decisions.

One the Thai side of that border, between 100,000 and 200,000 Cambodian refugees are huddled in squalor while the Thais feverishly try to feed their half-starved guests, some of whom have walked for a year across Cambodia seeking food and respite from embattled armies. Mingled among them are clusters of hard-bitten Pol Pot soldiers, regrouping before returning to the Cambodian battlefield. Their continued presence heightens the danger, since it could serve as an excuse to legitimize a Vietnamese move into Cambodia on the precedents of the Nixon-Kissinger invasion of Cambodia or Israel's incursions into Lebanon.

Though occasional Vietnamese shells fall on Thai targets, most observers doubt the Vietnamese will attempt an outright invasion, noting that the Vietnamese secretary of state for foreign affairs has told the Thai prime minister that Vietnam will not violate Thai territory. Yet such assurances may be only an inducement for a separate deal that would alienate Thailand from its nearby allies. The Vietnamese are demonstrably expansionist, while Moscow, which supports their aggressions and provides their military supplies, might well encourage them to overrun Thailand to extend Soviet influence throughout Southeast Asia and embarrass both China and the United States.

One can argue, of course, that the Kremlin's current caretaker government is in no mood for adventures and that, in swallowing Laos and Cambodia, the Vietnamese should be content to settle for control of the three nations that were once Indochina. But, though such arguments have logic, no one can be sure that the Vietnamese will behave according to our concepts of rationality. Since they have been fighting for over 30 years, two generations have known nothing but war. Who can say that such a warrior nation, made arrogant by its defeat of America, will be content to rest at the border?

Yet, if the Vietnamese do risk a crossing, how would we respond? The Manila Agreements (the current euphemism for the SEATO treaty) bind us in the event of armed attack against Thailand to "act to meet the common danger in accordance with [our] constitutional processes." But how can the common danger be effectively met? Though we are now speeding the supply of military equipment to the Thais, their army of only 140,000 men would presumably be no match for 600,000 Vietnamese. Nor could the Thais expect much help from nearby allies except moral and political support, which does not win wars.

We could, therefore, find ourselves with the choice of either intervening or letting Thailand be overrun. How many Americans would support a new war against Vietnam? Yet, if we did not effectively help Thailand, the other Southeast Asian nations would almost certainly make separate arrangements with Hanoi. If, after withdrawing from Vietnam, we should let another ally go under, Japan would inevitably be forced to reexamine its total dependence on our security commitments, which many Japanese are already beginning to question, and would be under irresistible pressure to build its own military forces and even to acquire nuclear weapons. America would lose its position in the Pacific, leaving the area a cockpit where China, The Soviet Union and Japan would struggle for power.

Whether or not we intervened, China could not, without loss of face, accept the expansion of an enemy neighbor to which it had tried to "teach a lesson," nor could it tolerate the threat of encirclement that would follow the increasing hegemony of Moscow's Vietnamese ally. Quite likely, it would find it more useful to attack Vietnam than to help the Thais, particularly since our American experience in Vietnam has demonstrated how hard it is to give military support to a nation not directly next door.

That, in turn, might lead to a Soviet reaction, for Moscow could hardly fail to aid its ally. It, too, might prefer to attack China from the north, rather than help the Vietnamese directly, while, at the same time, encouraging Kim II Sung to move against South Korea, in the confusion following the assassination of Park Chung Hee, thus distracting America further.

What I have described is, of course, a worst-case scenario, and I doubt events will follow such a bizarre and frightening course. Yet no one can be sure. The tangled skein of alliance that touch Vietnam and Thailand and involve all three superpowers might well produce a sequence of events having a momentum of their own, as happened in Europe in the fateful autumn of 1914. Just as tiny Serbia set off a world conflict, the small, irrational nation of Vietnam could, by an impetuous move, ignite an even greater conflagration.

We must, therefore, urgently concentrate on heading off the cataclysm. While hastening supplies to starving people on the Thai border, we should mobilize all diplomatic resources to disuade the Vietnamese from a supremely rash act. Time is clearly of the essence, since it is now the beginning of the dry season -- the classical period for fighting on the damp soil of Southeast Asia. We must move quickly.