(Updates with UK, US statements confirming move)
WASHINGTON, April 16 (Reuters) - The U.S. Defense Department has approved the first trans-Atlantic flight of Lockheed Martin Corp's F-35 fighter jet in July to take part in two international air shows near London, U.S. and British officials said Wednesday.
The new warplane will make its international debut at the Royal International Air Tattoo, or RIAT, an annual military air show held outside London in July, followed by appearances at the show, held every other year, said the officials.
"The U.S. and the UK have worked closely together on the F-35 project from the beginning. This fifth generation stealth combat aircraft will be a major boost to British combat air power and it is entirely fitting that the F-35's first stop outside the United States will be in the UK," British Defense Secretary Philip Hammond said in a statement.
Lockheed is the Pentagon's No. 1 supplier.
The jet's appearance will be closely watched by potential buyers, including Canada and Denmark, which helped fund the plane's development but are rethinking their procurements.
F-35 backers say the decision reflects growing confidence in the $392 billion program, the Pentagon's costliest weapons program, but skeptics say the plane still faces challenges with completing the software needed to integrate weapons on the jet.
Britain, which contributed $2 billion to the development of the new radar-evading fighter jet and plans to buy 138 F-35s in coming years, asked for the jet's participation to help showcase the increasing maturity of the new radar-evading plane. Britain was also the first international partner on the program.
Aerospace analyst, Richard Aboulafia with the Virginia-based Teal Group, said the F-35's first overseas appearance marked the start of a more aggressive drive to lock in foreign orders at a time when the U.S. military has repeatedly delayed its own.
"What they really need to do is transform the program's economics by getting above that 30-something (annual production) plateau they're on," he said. "They need to get to a virtuous cycle where numbers go up and costs go down ... the opposite of a death spiral."
Pentagon officials say they expect the plane's costs to fall to the mid-$80 million range by 2018 or 2019 from around $112 million now, and are working closely with the industry to drive the price down further.
But the Pentagon warned on Tuesday it would have to postpone orders for 17 more F-35s from fiscal 2016-2019 unless Congress reverses mandatory spending cuts due to resume in 2016.
Lockheed is developing three models of the F-35 for the U.S. military and eight international partners: Britain, Australia, Canada, Denmark, Norway, Italy, Turkey and the Netherlands. Israel and Japan have also placed orders, and South Korea has said it plans to order F-35s later this year.
Current plans call for several F-35s to participate in the air shows, including at least one of the three F-35 B-model jets already built for Britain, with a UK pilot at the controls.
U.S. and UK officials agreed on the need to bring over a number of aircraft to avoid any technical flight disruptions.
In 2011, Airbus' delayed and over-budget A400 military transport plane was forced to curtail its debut appearance at the Paris Air Show after the plane suffered a gearbox problem in one of its powerful turbo-prop engines.
U.S. defense officials said the overseas flights would be used for additional training and would help the F-35 program office learn how the plane's logistics, maintenance, aerial refueling, and security systems work overseas.
Pratt & Whitney, a unit of United Technologies Corp, builds the single engine that powers the plane. Britain's Rolls Royce Group builds the lift fan that enables the B-model of the F-35 to land like a helicopter.
Other major contractors on the F-35 program include Northrop Grumman Corp and Britain's BAE Systems.
(Reporting by Andrea Shalal; Editing by Doina Chiacu, Sofina Mirza-Reid and Bernard Orr)