TAIPEI, Taiwan — While China ramps up its missile threat, Taiwan's air defenses are getting shabbier by the day.

So says an unclassified report from the Defense Intelligence Agency, prepared for and sent to the U.S. Congress last month.

Taiwan has some 400 fighter jets, but "far fewer" than that number would actually be good in a fight, the DIA says.

(China has 330 fighters within range of Taiwan, and 1,655 fighters total, according to the most recent Pentagon report on China's military power).

Some of Taiwan's planes are too old, others have outdated gear. And for Taiwan's 56 French-made Mirage fighter jets, spare parts are in short supply. Afraid of China's wrath, France hasn't sold any major weapons to Taiwan recently, leaving the U.S. as Taiwan's only supplier of big-ticket arms systems.

The report also highlighted the growing missile gap between Taiwan and China. Despite warming cross-strait relations, China continues to build up its arsenal of short-range ballistic missiles (at least 1,300 and counting) and cruise missiles (several score).

To shoot those down, Taiwan has 200 Patriot missiles and 500 homegrown "Skybow" missiles, the DIA says. But Wendell Minnick, Asia bureau chief for Defense News, said in an email that only about half the Skybows can hit incoming SRBMs (the others can only be used against

aircraft), and "normally you dedicate 2 missiles per incoming target."

That means Taiwan can only blunt some 15 percent or less of China's deployed missile force.

Three hundred and thirty more Patriot missiles, and missile fire units, were approved by

Washington in 2008 but won't be delivered until August 2014, says the DIA. And the weapons package released for sale by the White House last month — the one China got so angry about — will add another 114 Patriots after that.

Even then, it's a lopsided game, and the Patriots and Skybows would be used to protect only the most valuable military and political targets.

China, for its part, has insisted its missile arsenal is there only to deter Taiwan's pro-independence forces from seeking a formal, legal break.

The DIA report comes as Taiwan and its allies in Washington push hard for President Obama to approve the island's request for 66 advanced F-16s to replace its over-the-hill fighters. Taiwan has been asking for the planes since 2006.

The DIA didn't openly push for the sale, but the implications of its report are clear. Says the report dryly, "Taiwan recognizes that it needs a sustainable replacement for obsolete and problematic aircraft platforms."

One interesting side-note of the DIA report was its inventory of Taiwan's tactical or short-range surface-to-air missile arsenal. It includes some 2,000 Stinger missiles, including 728 shoulder-fired units, and more than 700 other missiles.

Those wouldn't be any help against ballistic or cruise missiles. But if China's People's Liberation Army ever did attempt to invade and occupy Taiwan, they could be a "huge problem for [PLA] helicopters and low-altitude aircraft," said Minnick.