WASHINGTON (Reuters) - The Obama Administration has notified Congress of a possible sale to Turkey of advanced Patriot PAC-3 antimissile systems and related gear valued at up to $7.8 billion. The primary contractors would be Raytheon Co and Lockheed Martin Corp, the Pentagons Defence Security Cooperation Agency said in a notice made public on Friday. The proposed government-to-government sale would include 13 Patriot fire units, 72 Patriot Advanced Capability (PAC-3) missiles and a range of related hardware. Turkey would use the PAC-3 guided missiles to boost its missile-defence capability, strengthen its homeland defence and deter regional threats, the agency said. Turkey is a partner of the US in ensuring peace and stability in the region, it said. It is vital to the US national interest to assist our North Atlantic Treaty Organisation ally in developing and maintaining a strong and ready self-defence capability that will contribute to an acceptable military balance in the area. The proposed sale of this equipment and support would not alter the basic military balance in the region, the agency said. This would mark the first Turkish purchase of PAC-3 missiles, the notice said.