An Army private who returned to the West after defecting to the Soviet Union was ordered held in a secure military jail by a magistrate who said he posed a security risk and might try to flee. But Ronald Kuby, the civilian attorney for Pvt. Wade E. Roberts, called the ruling "punitive and unnecessary" and contended the 22-year-old Riverside, Calif., man was being penalized because his defection was to the Soviet Union. Roberts was arrested Nov. 4 shortly after returning to West Germany following an eight-month stay in the Soviet Union. He was questioned at Ft. Dix, N.J., then was transferred to the Philadelphia Naval Yard brig because of a 72-hour detention limit at Ft. Dix. During a 15-minute hearing, military magistrate Capt. Brenda Pifer decided Roberts should be held at the more secure brig rather than the minimum security detention area at Ft. Dix.