The Romanian government has awarded Rapiscan Security Products Inc., a wholly owned subsidiary of OSI Systems Inc., a $2 million order for a gamma radiographic detection system (GaRDS). The GaRDS is an advanced, self-contained, mobile gamma-ray imaging inspection system for screening trucks, cargo containers and passenger vehicles for contraband and explosives. Rapiscan said it will deliver the system early next year.   . . .   BAE Systems North America has appointed three presidents to lead business lines in its Information and Electronic Warfare Systems (IEWS) unit, headquartered in Nashua, N.H. Don Donovan was promoted from vice president to president of the IEWS Electronic Warfare/Electronic Protection business, which includes infrared and radio frequency countermeasures, the F/A-22 and Joint Strike Fighter and threat warning and defensive systems. Mike Heffron was promoted from vice president to president of IEWS Electronic Warfare/Information Warfare, and John Lydiard is now president of IEWS Mission Electronics, with responsibility for the company's mission electronics and infrared imaging systems areas.