UNHAPPY BOLIVIA -- poor and divided in the best of times, and now fallen into the hands of a junta with close ties to the international drug traffic. The Carter administration began cutting down its aid to Bolivia last month, a few days after the coup. Now the State Department is pulling out all of its narcotics control programs. "We have no basis to expect the kind of cooperation from the Bolivian authorities that makes it worthwhile to continue," a State Department official dryly observed.

Bolivia is becoming the nightmare state in which the underworld takes over the government. The process, incidentally, is not a gentle one. There are now perhaps 2,000 political prisoners, according to a leading clergyman, and the stories of sudden disappearances and torture are multiplying. That is why the new government has been harassing and threatening the few foreign news correspondents remaining in the country. It wishes to choke off all reporting of these practices.

Any country that organizes itself as a haven for criminal activity becomes a menace to all the others. If a clique of generals can seize a government, run up the skull and crossbones and turn their land into a pirate kingdom, they become an active danger to every other government struggling to enforce international law and, in this case, stamp out the drug trade. Unfortunately, Bolivia fits into a larger pattern.

South America is now divided, politically, into two zones. In a crescent along the north and west lie the three democracies, Venezuela, Colombia and now Peru. Below that line, the continent is ruled by military governments that vary only in the degree of their authoritarian repression. The first foreign government to recognize the new Bolivian regime was Argentina's, which has been providing generous aid and technical assistance to Boliva's secret police. Recognition came next from Brazil, which has been training Bolivian military officers. Then came Paraguay, a simple dictatorship in the style of the last generation.

Bolivia is conceivably the world's least stable state.

It has been through some 200 coups in its century and a half of independence. To explain the latest of them does not require any theory of foreign subversion. But to the extent that Bolivia's neighbors -- particularly Argentina -- now support the junta in La Paz, they must accept some measure of responsibility for the evils that will flow from its involvement in the drug business. Even Argentina's military men might ask themselves whether it's not a high price to pay for the stifled silence that now passes for political order in most of South America.