(Reuters) - Japan has opened talks with Western defense contractors about building a new generation of fighter jets, sources say, in what would mark an important milestone in Tokyo’s strategy to maintain its air superiority over rival China.

A prototype of the first Japan-made stealth fighter is pictured at a Mitsubishi Heavy Industries' factory in Toyoyama town, Aichi Prefecture, central Japan, in this file photo taken by Kyodo January 28, 2016. REUTERS/Kyodo/Files

The discussions with defense companies including Boeing Co and Lockheed Martin Ltd come as Japan readies its ATD-X experimental aircraft for its first test flights within days.

Stealth fighter technologies being tested on the ATD-X, being developed by Mitsubishi Heavy Industries (MHI) and the Japanese Ministry of Defence’s Technical Research and Development Institute, would also be incorporated into the new fighter, dubbed the F-3, industry and government sources said.

“They have begun exploratory engagement to look at our capabilities,” said a source with a Western defense contractor. “There is no policy decision and no program of record for the next fighter. There is only some discussion that, logically, there will be a fighter at some point.”

Analysts estimate the cost of such a program at $40 billion or more, a price tag that could yet prove prohibitive.

Japan has already committed to buying 42 Lockheed Martin F-35 Joint Strike Fighters. But that aircraft’s perceived shortcomings in air-to-air combat and the United States’ refusal to sell its Lockheed Martin F-22 Raptor have encouraged Japan to consider a domestic-led program to replace its fleet of aging Boeing F-15J warplanes.

Plans are likely to be firmed by end-2017 or early 2018, which would enable the F-3 program to secure funding in Japan’s 2018-2022 five-year plan and be in service by around 2030, the sources added.

Upgrades to a large portion of over 150 aging Japan Air Self Defence Force F-15Js, to incorporate new engines and radars among other advanced capabilities, could proceed while research into the F-3 program continues, said the sources.

Japan’s Defence Ministry said it was considering various options for future fighter jets “including independent development and international joint development” to replace its F-2 fighter fleet from about 2030.

It declined to comment on whether it had started discussions with western defense contractors.

CHINA FLYING HIGH

China’s development of modern and stealthy fighter jets, combined with Japan’s more muscular security agenda under Prime Minister Shinzo Abe, is fuelling Tokyo’s push for a new fighter.

As tensions between China and the United States and its allies rise in areas such as the East China Sea and South China Sea, Tokyo wants to ensure it can defend the airspace over Japan and its territories.

China’s warplanes still lag the best aircraft used by the U.S. and its allies, but Beijing has been building its capability, military experts say.

To maintain its air superiority, Tokyo had hoped to buy U.S. F-22 stealth fighters. Despite numerous discussions, however, Washington refused to sell, even to one of its closest Asian allies.

While the F-35s will replace some of Japan’s strike fighters, they are not a replacement for the F-15s in the air superiority role and don’t have the F-22’s capabilities, said one Japan-based source familiar with the thinking inside the country’s defense ministry.

“Japan really wanted the F-22 but it got the F-35,” added the source. “This is a source of concern and frustration in Tokyo.”

Japanese ministry planners believe that if the program goes ahead, the F-3 could be an aircraft similar to the F-22 in look and capabilities, said a second Japan-based source.

Manned and unmanned options are being considered, with a preference for the former, the source added.

Japan recently lifted a decades-long ban on arms sales and while the F-3 program is focused on domestic needs, exports of a home-grown fighter may also be considered.

Any joint effort could be similar to Japan’s F-2 program, where Lockheed Martin teamed up with MHI to develop a fighter jet based its F-16.

High development costs meant that the Japanese government paid around $120 million for each F-2, making it the second-most expensive fighter jet ever built after the F-22s at around $150 million each.

The basic F-35 model, by comparison, is expected to cost around $85 million each once full production is reached.

TOO COSTLY?

Some analysts believe the cost of developing an aircraft with the performance level of an F-22 may be a hurdle too high even for the world’s third largest economy.

“Paying for that performance difference by developing a new jet is simply too expensive. Where would Japan find $40 billion or more in its defense budget to develop a new plane?” said Richard Aboulafia, vice-president of analysis at Teal Group.

Help from Western firms could cut costs.

One potential partner was the Eurofighter consortium, a joint venture between Airbus, Finmeccanica subsidiary Alenia Aermacchi and BAE Systems that manufactures the Typhoon fighter jet, said sources. A Eurofighter spokesman declined to comment.

Lockheed Martin said it was very interested in working with Tokyo on the proposed F-3 program.

“Lockheed Martin has a very long history of developing new fighter aircraft, both indigenously and as a foreign partnership that incorporates leading edge technology to address emerging threats,” a spokesman said in an email.

Boeing’s record in developing new fighter jets can help any “ground-up” program, Jim Armington, who heads business development in East Asia for Boeing’s defense arm, told Reuters. Basing the F-3 on an existing design would give Japan a head-start, he added.

“Now, I can’t say which direction the Japanese government will go with this fighter, and whether it will be totally indigenous Japanese industry only or whether it will be opened up for foreign role and cooperation,” said Armington. “We are betting that there will be some opportunity for us to help.”