Returning from even a comparatively short stay in the People's Republic of China is like returning from the far side of the moon. That is true, at any rate, insofar as news of the outside world is concerned. What comes through in the official news service and in the mass circulation People's Daily is either limited and highly formalized or it is straight propaganda.

But extraordinary changes are taking place in China as it moves from a kind of massive hermit state to an active and aggressive participant in global politics. The best evidence is in the mission of Chairman Hua Kuo-feng to Romania and Yugoslavia in the Soviet Union's back yard. That is a long step from the volley of angry words fired at Moscow in recent years.

But Hua's journey is only one piece of evidence. As a slogan attributed to China's No. 2 man, Teng Hsiao-Ping, who is really running the country, puts it, "Let's have less stale rhetoric and more work."

That expresses the test China faces. The years of the Cultural Revolution were more than rhetoric, causing widespread damage to the structure of the nation's economy and to the men and women who were trying to sustain at least a semblance of a 20th century state. On one point almost everyone I talked with in China agreed: Another Cultural Revolution would end any hope of China's becoming a modern state. The question, then, is whether the forces of disruption have been contained.

The depradations of the conspiracy, led if only symbolically by Chiang Ching, Mao's widow, and the others in the Gang of Four, were accomplished by a constant barrage of rhetoric - a dogma intended to enforce a version of simplistic communism. Activists of the Gang of Four in many cities may be merely quiescent awaiting a new opportunity to assault the modernists.

The American position today in relation to the forces trying to push China out of the frozen posture of the past is extremely important. Along the way I have been re-reading a fascinating book about the American encounter with China. John Paton Davies Jr., in "Dragon by the Tail," gives in vivid detail from his own firsthand experience an account of the wretched muddle that led Washington to continue to pour billions into the bankrupt regime of Chiang Kai-shek while ignoring the honest reporting of officers in the field who correctly gauged the strength of Mao Tse-tung and the communists.

He saw America as a victim of the insularity and political immaturity of the American people and the unwieldy processes of democracy. With the collapse of Chiang Kai-shek's armies and his flight to Taiwan, as Davies and other officers in the field has clearly foreseen, the bitter infighting of who "lost" China ended with the sterile policy of trying to isolate the mainland under the pretense that the island of Taiwan represented all of China.

There was a slight advance with the "two Chinas" policy. But Peking would under no circumstances accept such a fiction. A shadow of that policy remains as opponents of normalizing diplomatic relations with the mainland insist on keeping the status quo with Chiang Kai-shek's son, Chiang Ching-kuo, as the ruler of Taiwan, with the tired pretense that he will one day return to govern all of China.

The opening to the world has potential dangers for the communist government. Thousands of young Chinese are being sent to study science and technology in German, France, Britain and the United States. Seeing the striking contrast to the austerity of their own way of life may undermine their loyalty.

But the forces of change that have been released cannot be reversed short of disaster and the return to a fragmented peasant-farm economy. That such a disaster would have a profoundly unsettling effect in the North Pacific cannot be doubted. It would give the Soviet Union the upper hand, and it could mean the two great communist powers coming together again.

That last seems highly doubtful, in light of the decade of hostility that has kept them at furious odds. But it cannot be entirely ruled out. In the beginning of a phase of profound change, of which the outside world is just becoming aware, anything can happen.

That was true during the Cultural Revolution. As one of the wise younger men put it, "anything could have happened." Part of that "anything" was ruinous civil war. Hua, Teng and the others charting a new course are confident that the corner has been turned and that they are on the way to a new China.