dubbed the FX, totals 42 planes, Japanese officials said. They didn't disclose the purchase price, but the order is expected to be valued at more than $4 billion, making it Japan's most expensive fighter procurement ever and one of the world's largest military contracts this year.

The Lockheed Martin jet won the contract over two lower-cost, combat-tested aircraft: Boeing Co.'s F-18 Super Hornet and the European consortium Eurofighter GmbH's Typhoon fighter. Those planes were seen to lack the stealth capabilities of the more advanced F-35.

Japanese officials justified the steep price tag by pointing to the increasing assertiveness of China and the technical advantages of the FX.

"We've seen a lot of changes in the regional-security situation, so we placed a high premium on the performance attributes" of the F-35 in its selection, Defense Minister Yasuo Ichikawa told reporters.

Lockheed Martin hopes the Japanese vote in favor of the F-35 will give it a boost in the U.S.—where its cost has attracted criticism—and in other nations considering an upgrade to their air-force fleet.

"Many countries will look at Japan's decision as a sign of the maturity of the F-35 program," said Dave Scott, director of F-35 international business development at Lockheed Martin.

Washington, Japan's chief security ally, had quietly pushed the case for a U.S. jet by highlighting the importance of interoperability, and the ability to share critical parts and conduct joint maintenance, say U.S. and Japanese officials.

In their decision, Japanese defense ministry and Self Defense Force officials cited the F-35's cutting edge technology, such as its so-called fifth-generation stealth design that provides radar-evading capability both in front of and behind the aircraft.

"The F-35 is the best fit for our defense needs," Shigeru Iwasaki, chief of staff of Japan's Air Self Defense Forces, told reporters after the announcement of the decision.

One potential source of controversy is the F-35's checkered development history, as the yet-to-be-deployed fighter has been dogged by repeated delays and cost overruns. Lockheed Martin has assured Japan that it can meet the country's procurement schedule, which calls for the first new fighters to be deployed by 2016.

The F-35 will replace the Japanese Air Self Defense Force's 70 aging F-4 fighters made by McDonnell Douglas, which is now part of Boeing.

Japan sees the jet's advanced technology as a way of deterring potential aggressors such as China and Russia, and to help foster the development of Japan's own aviation industry. In a key concession, Lockheed Martin agreed to license part of the F-35 production to a consortium of Japanese companies.

The Defense Ministry said that Mitsubishi Heavy Industries Ltd., IHI Corp. and Mitsubishi Electric Corp. will participate in production of the plane. Lockheed Martin and Japanese defense officials say details have yet to be worked out as to exactly how much of the plane is made in Japan.

Initially, Japan will purchase four F-35 jets made in the U.S., for which it has budgeted ¥13.7 billion ($175 million) each. Those costs are expected to decline as volumes increase, although some of the savings could be offset by Tokyo's plans to produce some parts domestically and assemble locally in Japan, where costs are higher.

The cabinet decision noted the amount of local production of the F-35 will depend on "current economic and fiscal circumstances."

The move to procure foreign technology comes as a tacit admission that Japan's own multiyear effort to develop a home-grown fighter is no longer a viable option, at least for the current generation of jet aircraft.

All told, Tokyo is prepared to spend a total of 1.6 trillion yen on the F-35 program, including equipment, spare parts and training costs, over the 20-year life cycle envisioned for the fighter, said Masaki Fukasawa, aircraft division director of the Japanese defense ministry's bureau of finance and equipment.

While the F-35 was the most expensive option by far, Japanese defense officials say the country's strategic needs outweighed the extra cost burden, noting the debut of two rival stealth prototype fighters: China's J-20 and Russia's Sukhoi T-50.

The long-awaited upgrade to the F-35 comes as China has ratcheted up its military spending, which is expected to rise 12.7% this year to 601.1 billion yuan. Meanwhile, Japan's defense budget—at ¥4.6 trillion this year—has declined for nearly a decade amid a ratio of debt to gross domestic product that has soared to 200%.