The father and sister of a Paraguayan youth who allegedly was tortured to death have filed a $10 million damage suit here against the alleged torturer. In an unusual legal action, the plaintiffs also asked that the Immigration and Naturalization Service not deport him until there is time for their suit to be heard.

The suit was served on Americo Pena-Irala at the Brooklyn detention center, where he is being held by immigration authorities who arrested him Wednesday and got a deportation order the following day.

Pena has been accused of human rights violations in Paraguay by the Organization of American States, members of Amnesty International and the Council on Hemispheric Affairs.

Pena apparently has made no move to resist deportation, but his accusers claim he would be immune from punishment if he returned to Paraguay, where he was a police chief inspector in the police-state government of Gen. Alfredo Stroessner.

When Pena was arrested, immigration authorities said he had been charded in Paraguay with the March 1976 torture death of Joelito Filartiga, 17. However, the dead youth's sister, Dolly Filartiga, says no formal charges were ever brought.

She and her father, Dr. Joel Filartiga, a well-known doctor and painter who has been jailed three times as an opponent of the Stroessner government, claim in their suit that the youth was killed "in retalation for the political activities and opinions of his father."

Their lawyer, Michael Maggio, says the suit could establish an important precedent-that human rights violators who came to the United States can be sued here by any of their victims who are also living in the United States.

Pena is charged here only wth overstaying his tourist visa.