A 15-year-old Arlington youth who pleaded guilty in the brutal beatings and robberies of two elderly women and robberies of two elderly women was sentenced yesterday to life imprisonment plus 60 years.

Arlington Circuit Judge Charles Russell expressed reluctance to impose such a heavy sentence on someone so young, but said he considered the defendent, Julian A. Morris, extremely dangerous. Morris was tried as an adult.

Late last January, Morris and a companion broke into the home of 72-year-old Lyda K. O'Donnell and threatened to kill her and her dog and burn her house down, according to prosecutors. O'Donnell was beaten unconscious and suffered a broken collarbone, arm and shoulder, nine broken ribs, a fractured eye socket, a punctured lung and severe cuts.She was found the next day lying under a pile of furniture.

Morris was also charged in an incident last Nov. 14 in which 80-year-old Susan C. Walker was left with a broken arm and robbed of $5,000 worth of furs, prosecutors said.

Morris pleaded guilty in July to two counts of burglary, two counts of malicious wounding, and one each of robbery and conspiracy.

Judge Russell gave him the life sentence on the robbery charge, 30 years for the two malicious wounding counts, 20 years for burglary and 10 for conspiracy.

Morris could be eligible for parole in 30 years.

Lionel Wormley, 16, tried as an adult, was found guilty of burglary, malicious wounding, robbery and conspiracy in the O'Donnell case and is awaiting sentencing. Robert Harris, 20, pleaded guilty to burglary, malicious wounding and robbery in the Walker incident as well as to receiving stolen property taken from O'Donnell's home. He also is awaiting sentencing.