FOR A YEAR China, a totalitarian communist state, has held open one forum in which citizens could have their individual say. On a dirty brick downtown wall, people have been able to put up big character posters for their fellow citizens and interested foreigners to see. There have been a few other outlets for public opinion, but none so important as "Democracy Wall." Most poster writers have confined themselves to particular grievances, as though addressing an ombudsman. But a few have ventured into frankly political terrain, criticizing official policies. This is, apparently, why Democracy Wall has now been closed down. Henceforth, to put up a poster, one must go to a park three miles out, register and be prepared to answer for "false charges" -- steps few Chinese are likely to take.

Students of totalitarianism can easily understand why the government moved. Democracy Wall provided a channel -- from posters, to reports by the foreign media, to broadcasts on the foreign radio stations beamed back into China -- by which Chinese who were so inclined could circumvent the controlled press and reach the Chinese public directly. This is a pattern familiar from the Soviet Union, and the Chinese could not have opened Democracy Wall without having been aware of it. At the start, the advantages of breaking old habits and enlisting the spirit of the people, especially educated people, must have seemed worth the risks of dissipating central control and permitting the questioning of official policies. But the process must have gone too far -- in somebody's view. It would be uncharacteristic too if factions within the leadership did not try to exploit the Democracy Wall channel for their own ends.

Should China be saluted for having kept this channel open as long as it did, or critized for having shut it down? The more interesting question goes to the foreign role in providing the means -- the correspondents and the radio stations -- by which Democracy Wall was transformed from a perhaps manageable one-block bazar to a finallly unmanageable national "parliament." Years of experience in the Soviet Union prove that to that question there is no answer equally satisfactory to both a communist government and the foreign press. The government's bottom line will always be control. The press's will always be openness. Some Americans, tickled to see American relations with China bloom and tending to feel that China was no Russia, may have thought it possible to pass by the difference. It's not.