A D.C. Superior Court jury began deliberating yesterday on whether 10 young persons are guilty of the 1984 killing of Catherine Fuller and recessed without reaching a verdict after three hours.

The jury of seven women and five men received the case after more than a month of often-dramatic testimony and after more than an hour of instructions from Judge Robert M. Scott.

Nine men and one woman, aged 17 to 26, are each charged with kidnaping, armed robbery and two counts of first-degree murder in what is believed to be the largest murder trial in D.C. history.

The defendants, most of whom are residents of Fuller's Northeast neighborhood, are accused of randomly picking Fuller, who was on a shopping trip, as someone to rob on Oct. 1, 1984. The prosecution said that the 48-year-old mother of six was followed and shoved into an alley near Eighth and H streets NE, where the group tried to steal her jewelry and the coin purse tucked into her bra. Witnesses testified that the 99-pound Fuller was repeatedly beaten and kicked as she fought back. Eventually, she was dragged over glass, nearly naked, into a litter-strewn garage where a foot-long pole was thrust into her rectum. She died of massive injuries.

If convicted of the murder charges, each defendant faces a mandatory prison term of at least 20 years before becoming eligible for parole.

Scott, in his instructions, warned the jurors to consider each defendant "as if he or she was being tried alone." He told them that if they wished they could return separate verdicts for each of the defendants as each decision was reached.

Scott also told the jury that it could convict any of the 10 defendants on a charge if they found a defendant had in any way "aided or abetted" one of the crimes. District law provides that a person can be convicted of felony murder if the person had participated in, encouraged or planned a felony that leads to a death, regardless of whether that death was an accident. Such direction was particularly important to defendants Felicia A. Ruffin and Clifton Yarborough, both 17.

Ruffin has been implicated in only the robbery. One prosecution witness testified Ruffin did not beat Fuller but received a ring that was taken from her. Several witnesses have identified Yarborough as a participant in the beating, but shortly after his arrest, Yarborough told police according to a videotaped statement that he was in the alley but only as a bystander.

Scott told the jurors yesterday that "mere presence" was not enough to convict a person of the crimes, but Scott said "mere presence" was "enough" if the person "aids or encourages" in any way, such as blocking an escape route.

Noting that the jurors had seen photographs of Fuller's battered body and that they heard a medical examiner testify about her extensive injuries, Scott cautioned the jurors not to allow the character of the charges to affect them.

Soon after they began their deliberations, the jurors sent Scott a note asking for copies of the testimony of several prosecution witnesses and for the medical records of one of the defendants, Alphonso L. Harris, 23.

One of the prosecution witnesses who implicated Harris in Fuller's death, Calvin Alston, said that he knew Harris because they played football together in the summer of 1984. Harris, however, testified that he did not know Alston and did not play football at that time because he was injured in two minor motorcycle accidents.

Before beginning instructions, Scott announced that an alternate had replaced one juror who had been removed at the juror's request "for personal reasons" unconnected with the trial. Sources said the juror asked that he be removed after a defense lawyer challenged the juror's neutrality during a closed courtroom session Friday