SHOULD JUVENILES from the age of 11 up be sent to adult jails? Prince George's County Circuit Court Judge Vincent J. Femia has started ordering certain young violators to serve up to 30 days in the county's adult detention center as a "shock treatment." And if the testimony of one such youth is typical, there's true shock attached: The judge ordered a 16-year-old to spend three weeks in the detention center in connection with an assault on an elderly woman and the snatching of her purse. After time in the jail, the youth told the judge that he had been terrified by the older male prisoners who threatened him continually, spat on him and tossed urine into milk cartons across a hallway into his cell.

That may be an extreme case, but it points up the sensitive nature of Judge Femia's decision to get tough - for there is a thin line between firm punishment of juveniles and excessively brutal treatment. It isn't that juveniles must be protected at all cost from going to jail; as Judge Femia notes, there are repeat offenders "who have committed the same criminal act time and time again and gotten their wrists slapped." Maryland's chief corrections officer, Mark Levine, agrees that the jailing of certain juveniles may help - if that action is used wisely. "If you have an individual who isn't responding to a program," Mr. Levine says, "we in corrections find it helpful to give them an idea of what it's like to be an adult."

Fair enough - but all too many adult jails today are ill equipped to accommodate juveniles. They are overcrowded - often mixing extremely dangerous criminals with inmates who belong in other types of correctional facilities and programs. To subject juveniles to those conditions is excessive. Similarly, we were disturbed by Judge Femia's treatment of another youth charged with lying to a police officer. The judge gave the 17-year-old a choice: seven days in jail or - here's the weird part - five strokes of belt from the youth's father. The youth chose the beating, which Judge Femia listened to outside the room.

If Judge Femia merely wanted to demonstrate that punishments of repeat offenders could be much tougher than they have been, he has made his point. But subjecting juveniles to physical abuse - by a parent or hardened adult criminals - has no place in the juvenile correstions system.