POOR BOLIVIA: it has tried so hard to climb back into the ranks of the Latin democracies, but, once again, it has suffered a relapse. This time the damage has been done by a colonel named Alberto Natusch Busch, who announced that he was suspending the constitution in order to serve the principle of constitutionality. The ousted democratic regime, installed a few months ago after a decade of military rule, had only a fragile hold on power. The civilian politicians, too little practiced in compromise, had been slow to settle things down. Talk of a coup had been rampant -- so much so in fact that, during his recent visit to La Paz, Secretary of State Cyrus Vance went to the length of inviting as many prospective coup-makers as he could for lunch at the American embassy to warn them off. Col. Natusch, who was invited, declined.

The special pity of this coup is that it did not result from a patent failure of the fledgling democratic government, which in any event had been in power too short a time to accumulate a list of serious shortcomings. It seems to have resulted chiefly from the machinations of Col. Natusch, who, if he represents any element at all, speaks for military men who faced the embarrassment of an official corruption inquiry. That leaves Bolivia's civilian politicians with a broad measure of common ground in opposition to his seizure of power. They can note, moreover, that it was precisely because of Bolivia's return to constitutional government that the country was singled out for praise at the recent meeting of the Organization of American States in La Paz, and that the OAS lent unprecedented support to landlocked Bolivia's longstanding appeal for an outlet to the sea. These international gains all stand to be lost under a renewed military regime.

When Col. Natusch declined Secretary Vance's invitation in La Paz last month and then made his coup, he indicated his contempt for the United States. It was fitting, therefore, that yesterday the administration cut off its aid programs. There was more than spite to this reprisal. Col. Natusch's hold is itself infirm. The civilian president he deposed is bravely insisting that he will not leave Bolivia. The elected parliament, though dissolved by the colonel, has said it will meet on Monday nonetheless. A state of siege has been announced, but peaceable demonstrations for the democratic cause are planned all the same. Other democracies in the Andean group have reaffirmed their support for constitutional government. Bolivia's democracy has certainly been hurt by the Natusch coup -- but the story is not over.