Singapore had shown interest in buying up to 100 of Lockheed Martin's F-35 Joint Strike Fighter aircraft over coming decades, matching Israel's tentative plans, the general in charge of the program for the Pentagon said.

The Pentagon's program chief, air force Major-Ggeneral Charles Davis, said the eight countries, including Australia, that had joined the United States to co-develop the plane appear to be largely sticking to their plans to buy about 730 of their own.

''The Israelis have said they'd take up to 100 aircraft,'' he said. ''The Singaporeans have said basically the same thing.''

Development of the F-35, a family of radar-evading aircraft, was co-financed by Australia, Britain, Italy, the Netherlands, Turkey, Canada, Denmark and Norway. Australia may also take up to 100 of the aircraft.

The US plans to buy 2443, including 1763 for the US Air Force, as part of its costliest arms acquisition program. Hundreds of others may be sold to other countries to replace a range of fighters.

General Davis said Japan would formally request F-35 pricing and availability information by the end of this year.

''There's no doubt it'll be a strong competitor'' in Japan, he said, adding talks had also taken place with Spain about the F-35 as a replacement for its Harrier aircraft.

He said the F-35 was on course to become a $US1trillion ($A1.04trillion) venture worldwide through to 2065, when the last to be built would reach the end of its projected service life.

It would cost $A1.04trillion ''to develop, buy, upgrade, sustain and fly more than 3000 fighter planes through their entire scheduled life cycle''. Reuters