"It is a key foundation for true jointness among our military services and it is further catalyzing interdependence with close international friends and allies," he said.

The United States and its partners last month agreed in principle to a long-term plan for how many fighters they would buy, but they are still working out details of a technology-transfer plan crucial to completion of the deal.

The draft pact includes statements of intent by the non-U.S. countries to buy a total 710 planes. The United States plans to buy 2,443, the first of which is due to be delivered to the U.S. Air Force in 2009.

The F-35 is designed to replace a wide range of existing aircraft, including the AV-8B Harriers, A-10s, F-16s, F/A-18 Hornets and Britain's Harrier GR.7s. The first F-35 is due to have its inaugural flight later this year, possibly by the end of October.