Ten senior enlisted men with top-secret clearances have been convicted in the theft of up to $50,000 worth of computers and tools at Norton Air Force Base and elsewhere, Air Force sources said. At least one civilian and an officer reportedly are still under investigation in the case that began with the scrutiny of 34 people. An Air Force spokeswoman said most of the merchandise, purchased from private outlets with government funds and appropriated for personal use, has been returned. Officials said there had been no breach of security. Most of those involved were stationed at Norton, near San Bernardino, and assigned to two top-secret units under the Air Logistics Command. Punishments have included reprimands, demotions, pay forfeiture, confinement, hard labor and bad-conduct discharges.