The arrest of former Mafia boss Tommaso Buscetta has given Italian authorities information about the inner workings of the Mafia, and it also has revealed Brazil's emerging role in the Latin American cocaine connection, in which he was deeply involved.

Brazilian federal police have begun the third phase of an operation to wipe out illicit plantations of coca in remote areas of the Amazon jungle. In two earlier operations codenamed "Frederico" in the Teffe region this year, they destroyed almost 9 million of the bushes that provide leaves for cocaine production and detected the beginnings of a shift of producers from the Andean countries into Brazil.

Buscetta was extradited from Brazil in July to answer charges related to heroin trafficking in Italy, and he also faces indictments in New York. But while in Brazil before he was arrested in October 1983 his attention clearly had shifted to the cocaine trade. Until 1972, when he first was arrested in Brazil, Buscetta allegedly ran a cocaine operation from a luxury villa near Sao Paulo called the Rancho Alegre -- the Happy Ranch. After he broke parole in Italy in 1980, Buscetta returned to Brazil and rebuilt his network based at Itatiaia, allegedly bringing cocaine base into Brazil from Peru and Bolivia with a fleet of light planes.

He was arrested after police found his Brazilian sportswear company was laundering drug money.

"We followed all his contacts, and when there was nothing new to learn we picked him up," said Hugo Povoa, head of Brazil's federal police drug squad.

In the last two years Brazil has acquired increasing importance as a corridor from the Andean producer countries, as political disturbances in Central America and a crackdown against traffickers in Colombia have made access to the United States more difficult, and traffickers make the connection via Europe.

"In geographical terms, Brazil is right between the producers and the consumers, with 16,000 kilometers about 10,000 miles of frontiers and the vast Amazon region," Povoa said in an interview. Now Brazil is also joining the ranks of cocaine producers, as the "Frederico" operations prove. Police have destroyed 8.6 million coca bushes and three laboratories this year, and 122 foreigners have been detained for deportation, including 45 Bolivians. Almost a ton of cocaine base also has been seized this year, according to police figures.

"We believe they wanted to transform Brazil into a major production center -- almost 10 million plants shows that intention," said Romeo Tuma, the federal police chief in Sao Paulo who coordinated Buscetta's arrest here in 1983. "Brazil is not yet producing the drug; they are still at the plantation stage," Tuma said.

In the operation police found signs that Peru's Sendero Luminoso guerrillas were using Brazil for refuge, according to Povoa. Peru's foreign minister, Luis Percovich Roca, claimed Sendero links with traffickers during debates on the drug problem at the General Assembly of the Organization of American States in Brasilia.

Tuma said the network of clandestine airstrips in the vast and almost unpoliced Amazon region, together with easy access by "mules," women who each carry in up to 10 pounds of the drug, has made Brazil an easy corridor to Europe for hard-pressed Colombian producers.

Tuma said that the Mafia's role in the cocaine trade had not yet eclipsed that of other Latin American groups, and by the time of his arrest Buscetta was still setting up a legal facade. "We were lucky as he hadn't yet built up extensive links," he said.

The full extent of Mafia operations in Latin America beyond Buscetta's immediate circle is still unknown, but police believe there could be up to four separate "families" represented in Brazil. Tuma recently traveled to Rome for talks with authorities.

The southern port of Santos has also become an important point for the arrival of base chemicals used by clandestine cocaine labs in neighboring countries. Last month police found a clandestine cargo of 100 tons of ether on a ship from Toronto, the third such find in as many months.

But authorization for searches is difficult because a treaty with Brazil gives Paraguay duty-free access to Santos. Officials found chemicals of European origin were being shipped to a non-existent firm in Paraguay and from there to Bolivia. Since 1981 Brazil has controlled production and sale of ether and acetone, and police have detailed maps showing the supply routes of these chemicals from Canada and West Germany through to Andean nations.

Claims that Brazil has become the major drug conduit or was an important link in Mafia operations have been viewed cautiously Drug Enforcement Administration officials at the U.S. Embassy in Brasilia. Nevertheless, the DEA recently sponsored a regional conference on drug traffic in Brasilia as part of new police cooperation between Latin countries, which began at a meeting in Bogota in August.

"There clearly are elements setting up in the Amazon, and the Brazilian police are determined to curtail that before it reaches major proportions," said a DEA offical, who requested that his name not be used. Although, he said, that there had been a "definite increase in the use of Brazil and Brazilian carriers as a corridor to Europe and the U.S., the main route is still direct from Colombia and Bolivia."

The DEA's tiny budget for operations in Brazil, just $250,000, reflects this. But next year it will rise to $1.25 million, in large part to finance eradication campaigns in the Amazon, which now rely on free use of helicopters boats and logistical backup from Brazil's armed forces.

"They've destroyed huge amounts of coca, which indicates Brazil is acquired importance as a cultivating nation month by month," the official said. "It's the start of a new period where cooperation between countries will have a definite effect on trafficking," he said.

Though officials welcomed the resolution by OAS member states meeting this week in Brasilia to hold a major conference on drug traffic in 1986 and to push for uniform legislation at an international level, they said the problem needed to be tackled urgently.

"This is an undeclared war, and some countries like mine are in the front line. This is a transnational phenomenon, which is destabilizing governments and creating economic chaos," said Bolivia's ambassador to the OAS, Fernando Salazar Paredes. Producer countries like Bolivia are also aware that consumption in the United States exacerbates their problem. "We're paying a high price in blood down here," Salazar said.