STATE OF SIEGE? In Chile? Again? There is a feeling that a familiar and tragic script is being played out once more in a country that barely endured it the last time around. Gen. Augusto Pinochet, who conducted the coup of September 1973, has reacted to months of widespread popular unrest and some terrorist violence not -- as he should have done -- by quickening the absurdly slow political liberalization on which he had embarked, but by closing it off. His long-threatened "hard hand" has produced a series of continuing arrests, the muzzling of the press, and the capture of the political parties. The elections he has been promising for some time appear even more remote.

What is wrong in Chile? Why is it just about the one Latin country, of the many which lapsed into military rule in the last generation, that has shown itse incapable of sustaining some sort of democratic revival? Two broad explanations are available. One goes to the personal style of Gen. Pinochet and emphasizes his combination of a hunger for power and an evident talent for adroit maneuver, which kept him the master of Chilean politics throughout the time he allowed liberalization to unfold.

The other explanation goes to the political culture of Chile. There is a painful lack of capacity among the parties to make serious coalitions, to compromise and to fence off the communist and fascist extremes. It is almost as though Chileans, having learned too little, were waiting to resume the political conflict that was raging, out of control, when the Pinochet coup broke it off 11 years ago.

The result now is a renewed state of siege, with many loud, bitter and ineffective complaints against it and with Gen. Pinochet claiming once again that he has saved the country from violence and anarchy, in short, from its own worst self.

This time, though, one element of special interest to Americans is different. A myth of American responsibility for the collapse of Chilean democracy spread in the 1970s. We say myth because the ever-expanding record makes it clear that Chileans were the architects of their own disaster, and the American role was, though often unwise and unhelpful, finally peripheral.

This time there cannot even be a suspicion of American involvement. The Reagan administration had moved American policy clearly away from the personalism and the distrust of democracy represented by Gen. Pinochet, although there was some backsliding the other day when the State Department could not bring itself to condemn the reimposition of a state of siege. In any event, the policy of supporting a return to democracy is the right policy and, if it is in heavy weather now, the fault lies again with Chileans.