A jury of seven women and five men was selected yesterday to hear the case against three Cuban exiles charged in connection with the 1976 car bombing assassination of former Chilean ambassador Orlando Letelier and one of his colleagues.

The jury was impaneled after four days of questioning of 153 prospective jurors by U.S. District Judge Barrington D. Parker and defense and prosecution lawyers in the case.

The jurors, along with six alternates, were immediately sent to their homes under escort of U.S. marshals to pick up personal belongings. The jury will be sequestered at an undisclosed hotel in the metropolitan area during what is expected to be a sixweek trial.

The three defendants on trial are Alvin Ross Diaz, Guillermo Novo Sampol and his brother, Ignacio Novo Sampol. Ross and Guillermo Novo are charged with the murder of Letelier and a colleague of his at the Institute for Policy Studies, Ronni K. Moffitt.

Ignacio Novo is charged with perjury in connection with testimony he gave a grand jury investigating the assassination and failing to tell the government about the crime.

For security reasons, none of the jurors' names will be disclosed, according to court clerk James F. Davey. But he said that the panel includes seven government workers, four people employed privately and one retired men.

Davey said there are four people in their 30s on the jury, two in their 40s, five in their 50s and one who is 63. There are two postal clerks on the panel, a D.C. police crossing guard, a D.C. government budget analyst, a laboratory technician, a D.C. government mechanic, a government food service worker, a nurse, a car cleaner, a packer, an electronics technician and a retired warehouse superintendent who once worked for the State Department.

It was believed that the jury selection, during which hundreds of questions were asked the would-be jurors, was the longest since the Watergate trial, when it took six days to pick a jury.

Defense lawyers used 15 of their 16 available peremptory challenges to jurors who were randomly placed on the panel. Prosecution lawyers used all eight of their challenges to remove jurors.

In addition, Judge Parker excused 51 possible jurors based on answers they gave him during questioning.

The government is expected to make its opening argument in the case on Monday.