PITTSBURGH (AP) _ A jury today decided that a 19-year-old man should die in the electric chair for the deaths of an elderly couple who were tied to chairs in their home and stabbed.

Christopher Caldwell, of Pittsburgh, confessed to police a year ago today that he killed the couple when a companion refused to do so. On Saturday, he pleaded guilty to two counts of homicide.

He sat quietly at the defense table as the jury foreman read the verdict.

''I think a lot of people in Allegheny County thought that should be the verdict,'' said Assistant District Attorney Christopher Conrad.

Caldwell said he was among five youths who broke into the home of Boykin Gibson, 88, a retired hotel doorman, and his 85-year-old wife, Sara. The Gibsons were tied with clothesline in chairs facing each other. Their throats were slashed and they were stabbed in the chest.

All five youths lived in the Gibsons' neighborhood, and some of the youths knew the couple, prosecutors said.

Caldwell carried a Bible with him to the witness stand when he told the jury of his remorse for having wielded the 8-inch knife despite the couple's pleas.

He testified that he cooperated with police ''because I couldn't run from what I had done. I couldn't run from myself.''

His attorney, Paul Gettleman, said before the death penalty verdict that he thought a guilty plea might avert such a sentence.

The judge is bound by the jury's decision.

The sentence will be imposed formally at a hearing Feb. 18 before Allegheny County Judge Robert E. Dauer. A number of appeals are expected before the sentence would be carried out.

Caldwell confessed to police Jan. 16, 1985, the day after the slayings. He said that after a companion refused to kill the Gibsons, he did so himself so the couple could not identify the group.

After hearing Caldwell's guilty plea, Dauer determined the degree of guilt to be first-degree murder.

Alan Williams, 21, who had refused to use the knife, was convicted at a trial and was sentenced to two consecutive life terms.

The other defendants - Alton Smith, 15, Eric Anderson, 19, and John Morris, 16 - pleaded guilty to third-degree murder and other charges and were to be sentenced after Caldwell's trial.