A former Paraguayan police official and his mistress, who are charged with a torture-murder in Paraguay, were arrested in Brooklyn today, the Immigration and Naturalization Service announced.

Americo Pena, 45, and Juana Bautista-Fernandez Villalba, 41, were arrested by investigators at the INS antismuggling unit and charged with overstaying their tourist visas, according to George Vician Jr., acting director of the New York district office.

Pena and Villalba became the center of a controversy in Paraguay following the March 1976 death of Joelito Filartiga 178 the son of a prominent philanthropist, doctor and painter.

The Organization of American States, Amnesty International and the Council on Hemispheric Affairs looked into the death after the father, Joel Filartiga, displayed his son's scarred body and appealed for help in prosecuting those responsible.

Richard Alan White, a seniro fellow of the Council on Hemispheric Affairs, issued a statement today describing Pena as "among the most detested and feared Paraguayan government officials" because of his activities as a police inspector in the Paraguayan capital, Asuncion.

White said that it was generally understood in Paraguay that Pena was involved in drugs and prostitution, and predicted that further investigation of Pena "will very likely reveal a sordid story of drug sales and the bringing into the New York area of unsuspecting Paraguayan teen-agers who were immediately forced into prostitution."

Pena was arrested after a tip from members of the Paraguayan community in New York last month led investigators to 1865 52nd St. in Brooklyn, where he has been living, the INS said.

Immigration authorities are holding Pena on $75,000 bond and Villalba on $25,000 bond pending deportation proceedings. A first hearing has been scheduled for Thursday.

Pena, Villalba, their 3-year-old son and a 16-year-old niece of Villalba entered the United States as tourists using their real names last July 21, according to the immigration service. The boy and the niece are not charged, and arrangements were being made for a social service agency to house them temporarily, immigration officials said.

A spokesman for the Paraguayan consulate general in New York said he had not been informed of the arrests or approached concerning the return of Pena and Villaba to Paraguay.

Initially, Pena was not charged with the kidnaping, torture or murder of Joelito Filartiga. Pena held the rank of inspector at the time of the killing, and the government of Gen. Alfredo Stroessner declared that no police participate in the crime.

Pena was promoted to chief inspector, but the international publicity organized by the dead youth's wellknown father apparently led to Pena's being charged and forced to leave Paraguay.

A Jan. 31, 1978, Organization of American States report on human rights in Paraguay mentioned the case, and described Pena as the man alleged to have planned the kidnaping and torture. The report said the OAS has photographs of the mutilated body of Joelito Filartiga.

Sources said there had been personal animosity between Pena and the Filartiga family for some time before the murder. The victime's father was known as a dissident in a country and Filartiga lived two houses apart in Asuncion.

Sources said Pena is believed to have continued to draw his police salary while living in the United States, and they accuse him of helping to transport young Paraguayan women to New York to work as prostitutes.

An immigration official said Pena did not deny his identity when he was apprehended by investigators this morning while on his way to a job he had taken as a wood finisher in downtown Brooklyn. The official added that Villalba was employed as a sewing machine operator and that the niece apparently was brought to the United States as a babysitter for the 3-year-old boy.