(Adds Raytheon, Lockheed comments, context)
By Mike Stone and Andrea Shalal
FARNBOROUGH, Britain, July 16 (Reuters) - The U.S. State Department on Monday said it was working with NATO ally Turkey on the possible sale of a Raytheon Co Patriot missile defense system to avert its purchase of a Russian-made S-400 system.
Tina Kaidanow, Acting U.S. Assistant Secretary of State for Political-Military Affairs, told reporters at the Farnborough Airshow that U.S. officials were "trying to give the Turks an understanding of what we can do with respect to Patriot." She did not say if the delegations were meeting at the air show.
Turkey had passed over the Patriot system twice in its selection process, first choosing a Chinese system, then turning to the Russian S-400 system in 2017.
Industry executives said Turkey had sought more technology transfers than Washington was previously willing to approve.
U.S. and NATO officials have repeatedly warned Ankara that the Russian system cannot be integrated into the NATO air and missile defence system, and its purchase would jeopardize Ankara's purchase of Lockheed Martin F-35 fighter jets.
Assistant Secretary of Defense Kevin Fahey, the Pentagon's most senior official weapons buyer at the show told reporters at the show that "Turkey has had an interest in Patriot, so we've been working for a while how we can make that work."
Kaidanow said Washington was worried that U.S. allies purchasing Russian systems would support "some of the least good behavior that we have seen from them (Russia) in various places including Europe but also elsewhere."
She said Washington wanted to ensure that systems acquired by U.S. allies "remain supportive of the strategic relationship between us and our allies, in the case of Turkey that is Patriots."
In April, the Trump administration rolled out a long-awaited overhaul of U.S. arms export policy aimed at expanding sales to allies, saying it would bolster the American defense industry and create jobs at home.
Wes Kremer, who heads Raytheon's Integrated Defense Systems business, welcomed the Trump administration's greater engagement on a possible sale of Patriot to Turkey.
"Turkey is an example of where this administration has engaged ... to get the U.S. systems out there," he said.
Lockheed Martin Corp, which makes the interceptors for the Patriot system, said one approach could be to offer Turkey an open architecture system like the Medium Extended Air Defense System (MEADS) it developed with European missile maker MBDA, which would allow Turkey to integrate its own missiles.
"Turkey has a fairly well developed industrial infrastructure," Lockheed's top missile defense executive said. "They have their own indigenous interceptors that could be integrated, if we can move to something more of an open system." (Reporting by Mike Stone and Andrea Shalal in Farnborough; Editing by Mark Potter, Jane Merriman and Richard Balmforth)