Some of their activities are described in this interview [0]. The claims come from 2015 not from the Cold War. And they're from a communist intelligence defector, not America.
There's no shortage of interviews from former intelligence people talking about Cold War era South America and much of it is well known. The basic gist is it was before modern ICBMs, the USSR wanted nuclear missiles close to the US and they wanted military bases there. This is where the FARC, Fidel Castro, Che Guevera etc all come from. And famously it's what led to the Cuban Missile Crisis and Bay of Pigs Invasion. A lot of this can best be understood in the context of what ideas the Soviets were promoting in other parts of the world, like revolutionary Islam.
There are also many essays on the connections between Marxism and liberation theology, many (maybe most?) of them written by liberation theology proponents during the Cold War years.
Some of the claims made in the interview
> On October 26, 1959, Sakharovsky and his new boss, Nikita Khrushchev, came to Romania for what would become known as "Khrushchev's six-day vacation." He had never taken such a long vacation abroad, nor was his stay in Romania really a vacation. Khrushchev wanted to go down in history as the Soviet leader who had exported communism to Central and South America. Romania was the only Latin country in the Soviet bloc, and Khrushchev wanted to enroll her "Latin leaders" in his new "liberation" war.
> The movement was born in the KGB, and it had a KGB-invented name: Liberation Theology.... The birth of Liberation Theology was the intent of a 1960 super-secret "Party-State Dezinformatsiya Program" approved by Aleksandr Shelepin, the chairman of the KGB, and by Politburo member Aleksey Kirichenko, who coordinated the Communist Party's international policies. This program demanded that the KGB take secret control of the World Council of Churches (WCC), based in Geneva, Switzerland, and use it as cover for converting Liberation Theology into a South American revolutionary tool. The WCC was the largest international ecumenical organization after the Vatican, representing some 550 million Christians of various denominations throughout 120 countries.
and so on.
There are lots of details you can check out and try to fact check. But it would be a research project and my guess would be hardly any of the classified information is public now. As a general rule, we get books and interviews from defectors and former intelligence officers, but they're based on first-hand recollection and contemporaneous notes backed by still-classified information.
So it's up to you to decide how much weight to give the various pieces of evidence. But certainly what he says in the interview is consistent with how the KGB operates. But we can't know things like whether he was lied to by the KGB at the time, or whether he's misremembering facts, or whether he's embellishing here or there.
[0] https://www.catholicnewsagency.com/news/31919/former-soviet-...