Last month, a coterie of generals suffocated democracy in Bolivia. It was a brutal coup that had the secret backing of the military rulers across the border in Argentina. It was a sad setback for free government in Latin America.

Calamities and coups have become commonplace in Bolivia, a piece of earth abused by man and nature. Those Bolivians who have clung to the mountain slopes are a simple but stoic people, more Indian than Spanish in ancestry, who scratch the gray, rocky soil for meager subsistence. For most of them, life is labor, and death comes early.

The succession of dictators who have ruled them have made their lives even more harsh and oppressive. But last month, it looked at last as if a constitutionally elected president, Herman Siles Zuazo, was about to take power. Until the coup on July 17, the outlook for civilian rule in Bolivia was optimistic.

An interim president, Lidia Gueiler Tejada, was ready to hand over the government. Then a military clique, headed by Gen. Luis Meza Garcia, seized power at bayonet point. A sad Lidia Gueiler was compelled to deliver the government to the junta. "God save Bolivia," she said mournfully.

The Argentine generals have denied reports that they intervened. But this is not the word that has reached the State Department. Sources in high places, who for diplomatic reasons don't want to be identified, contend the coup could not have occurred without the foreknowledge, secret support and military planning of the Argentinians.

"You won't find a smoking gun there," one source told my associate Bob Sherman, "but what you will find is a weapon with Argentina's fingerprints all over it." Here are some of those identifying prints:

Prior to the coup, Argentina increased the size of its mission in the Bolivian capital of La Paz. "They did it slowly at a time when people weren't paying much attention to them," explained an observer.

"It was an Argentine-style operation and not Bolivian," said another insider. "It was very well planned and that in itself is not Bolivian." During the first 24 hours of the takeover, the military rounded up 1,000 people and eventually arrested 2,500 potential opponents. "The roundup was very brutal," related an eyewitness. "Within 24 hours, they had neutralized the leadership and the opposition. Those who weren't in custody went into hiding or sought asylum, and others just disappeared -- Argentile style."

Some Bolivians who were released after the roundup reported that during their interrogation, men with Argentine accents dressed in civilian clothes appeared to be directing the Putsch.

Argentina unhesitatingly became the first foreign government to recognize the new regime. In contrast to the United States, which withdrew its ambassador and cut off all aid, the Argentine militarists offered economic assistance. The Bolivian generals asked for $200 million in foreign help, and Argentina's President Jorge Videla pledged to respond.

A top American official called the Argentine role a clear case of meddling in the affairs of its neighbors. "The Argentinians have a history of this," he said. "They intervened in Uruguay a few years ago, and they don't hesitate to move into another country if it serves their interest."

Larry Birns, director of the Council on Hemispheric Affairs and a critic of the Argentine ruling clique, said the junta has followed a policy that "the only acceptable government on its borders is one that it controls." In Birns' view, the collapse of the Bolivian democracy of the northern regimes and the back gate to the authoritarian regimes in the south," he explained. "It is a very pivotal place."

Apologists for Argentina have argued that Bolivia under a left-of-center democracy would have become a sanctuary for guerrillas opposing the Argentine military government. But a Washington official scoffed at this as political paranoia.

"The Argentines fear the cancer of communism," he said. "Their remedy is immediate-removal surgery. They always fear that their neighbors will harbor subversives. Bolivia is an unlikely threat. The Montenero guerrilla movement is an urban, not a rural group. The idea that Bolivia would become a base for subversion is unlikely."

Footnote: A spokesman for the Argentine Embassy replied to my reporter's inquiries with a prepared statement that denied that Argentina "may have interfered in any way in the events that recently took place in Bolivia." As a matter of principle, the statement declared, Argentina does not interfere in the internal affairs of other sovereign nations.