BERLIN (Reuters) - The U.S. military and European operators of the radar-evading F-35 fighter jet have agreed to work together more closely to help lower the cost of operating the new warplanes as growing numbers arrive in Europe, officials said.

FILE PHOTO: A Lockheed Martin F-35 aircraft is seen at the ILA Air Show in Berlin, Germany, April 25, 2018. REUTERS/Axel Schmidt/File Photo

Operating costs were a big issue when senior military officials from the United States, Israel and F-35 user nations in Europe - Britain, Italy, Norway, Denmark, Turkey, the Netherlands - met in Germany last week, they said.

“We discussed the importance of ensuring that future costs - specifically for sustainment - are kept to a minimum so that we don’t have to cut into future purchases,” U.S. Air Force Colonel Leslie Hauck, who heads the fifth generation integration office at the U.S. Air Force headquarters in Europe, told Reuters.

U.S. Air Force Chief of Staff General David Goldfein this year launched a big push to drive down the cost of flying and servicing the Lockheed Martin Corp LMT.N jets to the same levels as current fighters without stealth capabilities.

Experts say the Air Force - the biggest buyer of the F-35 - could cut back its planned purchase of 1,763 aircraft unless it can lower the cost of flying the world’s most advanced fighter aircraft.

The latest Pentagon selected acquisition report on the program put the cost per flying hour of the F-35 at around $30,000 per flying hour in 2012 dollars, compared to around $25,500 per hour for an older-generation F-16 fighter. Fuel cost changes could boost that sum in inflation-adjusted dollars.

The cost of buying new jets has come down and is expected to reach $80 million per aircraft by 2020, but more work is needed to reduce the cost of operating the jets, Hauck said. He said the Air Force wanted to cut the operating cost by 38 percent.

He said air chiefs from the user nations discussed the issue at the Royal International Air Tattoo, the world’s largest military air show, in England in July, and it would be a key focal point during a working-group meeting in November.

The Pentagon’s F-35 program office last week said it would compile and distribute information from users about maintenance procedures, staffing requirements and other key metrics.

“There are things that we can do with our group. But there’s not a good mechanism now to share the lessons learned,” Hauck said, noting that his office was also reaching out to F-35 users in Asia - Japan, Australia and South Korea - for their input.

Together the allies will have some 64 F-35s in Europe by 2019 and 550 by 2034, General Tod Wolters, the head of U.S. and NATO air forces in Europe, told officials at last week’s meeting. The first U.S. F-35s are set to arrive in 2021.