THE important question about President Reagan's trip to China is not what he will do to China, but what China will do to him. He will do almost nothing to China. The agreements he will sign have been prenegotiated. The only effect his actual visit can have on Chinese policy and on the attitude of Chinese leaders toward him and his country is whether they conclude that they can count on him to pursue a consistent attitude toward them.
They long since took up a tentative position on this point. They assumed that once he decided to seek improvement in the relations between the two countries, he would stay with it. Without this assumption they could not logically have allowed him to make this visit.
There is little reason to doubt that during the course of the visit the Chinese will conclude that he has become as emotionally committed to dealing with them as he was emotionally committed the other way before he got to the White House and began to listen to the arguments for changing his mind.
Those who of late have heard him talk about China report that he now waxes as eloquent about the chances for increasing American sales to China as he ever waxed in older times about the superior virtues of those Chinese who live on Taiwan. His pro-Taiwan stance at the beginning of his administration was a major cause of trouble between the White House and his first secretary of state, Alexander M. Haig Jr. It was one reason for the Haig departure.
The most solid reason yet for the theory that Mr. Reagan can and does change his mind and that he is educable about the big outside world is that as late as 1982 this trip would not have been conceivable. Today it is not only conceivable , it is actually happening. The question is whether what Mr. Reagan will see and hear there will have a further impact on his thinking.
It can make a further difference. Once you have seen the Roman Forum you have a new sense of why Rome influences Western politics and culture to this day. To see the Kremlin is to change your perceptions of Russia and Russians. To visit the Forbidden City in Peking, to climb the Great Wall, to explore the Ming tombs and the buried army of clay soldiers at Xian, does something to people.
Mr. Reagan has for most of his public life assumed that communism and Soviet influence are identical and that if the first comes in the door the second will follow. His attitude toward the Middle East and his policies toward Latin America are grounded on that assumption. He is waging a major undeclared war against the government of Nicaragua on this precise assumption. He assumes that as long as Nicaragua remains under Marxist influence it will be an agent of the Soviet Union in Central America and that if the Marxists triumph in El Salvador, it too will become a military outpost of the Soviet Union.
There is no questioning the fact that China is a Marxist state run by confirmed Marxists. The leaders proclaim their loyalty to the doctrines of Karl Marx. Even when they experiment with private-enterprise economics, as they are doing these days, they justify it in the name of Marxism. True, they rewrite the book from time to time. And true, the Soviets call them heretical Marxists.
But the leaders of China today are as Marxist as they know how to be. They run a tough, often ruthless dictatorship under a one-party system. And they are not agents of the Soviet Union. Their frontier with the Soviets is heavily manned. There has been border fighting between the two off and on for roughly 20 years. They claim much territory once Chinese which is now under Soviet rule.
Mainland China has been proving for almost a generation that communism and Soviet influence are not identical. Yugoslavia has been proving the same since Tito's break with Moscow in 1948.
To visit either China or Yugoslavia is to learn that a country can live by its own definition of Marxism, or communism, and be fiercely independent of Moscow.
Will Mr. Reagan acquire some realization of this condition from visiting China and talking to no one but communists while he is there? If he does it might make a difference in his thinking about other parts of the world - including Latin America.