The cases of two 17-year-old Tarzana youths who were arrested in May on bank-robbery charges have been extensively covered in local newspapers, including the San Fernando Valley edition of The Times. As a result, Judge Burton S. Katz of the Sylmar Juvenile Court feared that the publicity would hamper the youths' ability to get a fair trial. So he barred the press and the public from pretrial proceedings and slapped a gag order on participants in the case, forbidding them to discuss it in public. He further ordered the press not to try to contact persons attending the hearings. On reflection, though, he realized that the second order was both unconstitutional and unenforceable, and he set it aside. He should have set aside the other orders, which are on appeal.