They are veterans of a long, lost war, the five Cubans indicted yesterday in connection with the slaying of a former Chilean ambassador. Though some of them led outwardly calm, industrious lives, they were also familiar with the darkest sides of life in the Cuban communities of New Jersey and Miami.

Among the most radical, right-wing elements of those communities, conspiracy often blends with intense desire to return to a Cuba purged of Castros revolution, and passions burn like fuses.

It is also a world of secrecy from which there erupts occasional, sometimes spectacular, outbursts of violence.

Some of the first names to come to light in the investigation of Orlando Letelier's murder were those of the Novos - Ignacio Novo Sampol an unemployed shoe and auto salesman, and his younger brother Guillermo Novo Sampol. They were implicated by another Cuban exile leader who was being held in Venzuela at the time in connection with the bombing of a Cuban commercial airliner in which 73 persons died.

The Novos were leaders of the militant Cuban Nationalist Movement based in Union City, N.J., and their names had long been familiar to the federal agents who keep an eye on the exiles' counter-revoluntary underworld.

It was the Novo brothers who were charged in 1964 with firing a bazooka at the United Nations building while Cuban revolutionary Che Guevara was speaking there, though the charges later were dropped.

Ten years later, Guillermo Novo was convicted of plotting to blow up a Cuban ship anchored in Montreal.

By April of last year, another member of the Cuban Nationalist Movement was drawn into the investigation. But, even though he was offered immunity for his testimony, 38-year-old salesman Jose Dionisio Suarez Esquivel, of Elizabeth, N.J., refused to talk, and spent 11 months in jail.

Both the Novos and Suarez testified under oath that they knew nothing of Letelier's murder.

According to yesterday's indictment, however, Guillermo Novo, Suarez, and their compatriots, Virgilio Paz Romero and Alvin Ross Diaz met with DINA agent Michael Vernon Townley on Sept. 13, 1976, to plot the murder of Orlando Letelier.

By Sept. 18 the same four members of the Cuban Nationalist Movement had helped Townley construct a bomb, according to the indictment.

On Sept. 21, Letelier died when a bomb blast destroyed his car.