We will never know what would have happened if President Reagan had decided to ignore warnings from Peking and had allowed the Nationalist Chinese on Taiwan to buy military aircraft far more modern than any possessed by the mainland Chinese.
There are two schools of thought in Washington about what would have happened.
One school, mostly among Republican politicians, argues that China gains more than the US does from the US-Chinese relationship. Therefore, the adherents of this school think, Washington can sell anything it likes to Taiwan and the men in Peking will do nothing but huff and puff.
The other, dominant school, which includes most of the China experts in the State Department and at the Central Intelligence Agency, worries very much about what might have happened. It holds that an era of American foreign policy, dating from President Nixon's trip to Peking in 1972, might have gone down the drain. It might even have meant a new regime in China seeking to return to the old days of the Chinese-Soviet alliance.
The professional worry was based on doubt that the political situation in China has yet settled down into a long-term post-Mao pattern. They think that there are political elements left over from the ''great Cultural Revolution,'' the ''Red Guards,'' and the ''gang of four'' who are dissatisfied with the present system dominated by Deng Xiaoping. They think these others are active behind the scenes and would, if the opportunity occurred, be delighted to undermine or unseat Deng.
Deng is the political heir of Chou En-lai, who masterminded the turn away from the ideological radicals of the Cultural Revolution. It was Chou, aided by Deng, who executed the reopening of relations with the US. Chou and Deng were the pragmatists who felt that modernization of China was more important than ideological purity. So long as Deng is the real power in Peking, it is likely that relations with the US will be kept reasonably friendly and easy.
But what if the political descendants of the gang of four should manage to topple Deng in a palace revolution?
Certainly no one in the outside world can be sure of the answer. If the ''gang'' came back, there would not necessarily be a reopening of Chinese relations with Moscow. But the ideologues of the radical left in China are passionately anti-American. It seems unlikely that the kind of easy relationship between Washington and Peking that has prevailed since Richard Nixon went to China would flourish in a post-Deng era.
If Mr. Reagan in Washington had decided to sell the latest American military weapons to Taiwan, the enemies of Deng would have had a political weapon to use against him. Might they have unseated him with that weapon?
That depends on how solid or weak is the political ground in Peking. That matter cannot be judged with confidence in Washington. But there was certainly a risk inherent in the decision.
Had it gone in favor of dispatching the modern weapons to Taiwan, the pattern of world relations that began with the Nixon trip to China might have come undone. The world could then have returned to the earlier condition in which the US faced a hostile coalition of the Soviet Union and China.
Besides, which country -- the US or China -- does gain the most from the consequences of President Nixon's trip to Peking?
It is easy and perhaps comforting in Washington to think that China gains the most, hence can be treated in a cavalier fashion. But there was once a time when the Soviet Union and China were formal allies and Moscow enjoyed the dominant political position in the world. Its influence stretched from the Elbe in the heart of Europe to the China Sea. It ruled what the geopoliticians have long called the ''heartland'' of the world.
During those days the US felt that it needed to be strong enough to wage war against China and the Soviet Union at the same time -- and have a little left over for dealing with Fidel Castro's Cuba if worse came to worst. The US maintained in those days a standing armed force of 3.5 million men. There was concern lest even this was enough to handle what might happen.
The world has been a safer one for the US and its friends from the day Nixon went to Peking. Moscow's military power has increased, but its freedom to dispose of that power has declined. In the pre-Nixon-to-China era the US had to deploy roughly half of its military power in the Far East against China. Since then it has been able to deploy less power more flexibly.
Its armed forces are down by more than a million men from their earlier peak of 3.5 million. But little or nothing is needed to watch the Chinese. Most of it is today deployed either on the NATO front in Europe or in the Middle East trying to protect access to the oil of Arabia.
Would it have been prudent for Washington to risk this favorable situation for the sake of pleasing the people on Taiwan, who are not under any immediate threat from the mainland anyway?
Perhaps the mainland Chinese might entertain aggressive intentions toward Taiwan had they the ability to cross the Taiwan Strait. They do not have that ability. Nor do they possess enough sea lift to get a substantial landing force to Taiwan. They do not have the long-range air power that could cover such a crossing. Taiwan is safe with the defensive aircraft Reagan is happy to let them go on buying.
The above is the background for the decision the President announced on Jan. 11. It disappointed the government on Taiwan. It disappointed the Northrop Corporation, which had hoped to sell a new model fighter plane to Taiwan. But it avoided the risk of upsetting the power balance that has existed to the advantage of the US ever since Nixon reopened relations with mainland China.
The Chinese-US relationship has not been entirely placid since. The announcement on Jan. 11 was made hurriedly because of ''leaks'' to the press. It was made unilaterally in Washington instead of having been made in concert with the Chinese. The Chinese have complained, loudly, against any ''unilateral decision,'' and about the sale of any US weapons at all to Taiwan.
The complaints were made on Jan. 12, the day after the Washington announcement. Since then, and at least up to the time this goes to press, there has been no further ruffling of the waters of US-China relations. Previously there had been hints that the Chinese might downgrade the relationship by recalling their ambassador from Washington and sending home the US ambassador in Peking.
Perhaps they have decided that further gestures of disapproval would serve no further good purpose. Nixon's power world seems to have survived the Taiwan episode.