BEIJING—China's first test flight of its stealth fighter Tuesday overshadowed a mission to China by U.S. Defense Secretary Robert Gates to repair frayed military relations, and prompted concern about whether President Hu Jintao and the civilian leadership are fully in control of the increasingly powerful armed forces.
U.S. officials said that President Hu appeared to be taken by surprise when Mr. Gates asked him about the test flight during a meeting, hours after pictures and accounts of it began appearing online.
Analysts said that would be an embarrassment for China's top leader—who in theory controls the military as chairman of the Central Military Commission—just as Chinese officials anxiously try to make sure Mr. Hu's planned trip to the U.S. next week goes smoothly.
If the military deliberately kept Mr. Hu in the dark, that would reinforce concerns that hawkish elements in the military are increasingly driving China's foreign policy—including ties with the U.S.—and that they are trying to enhance their power in China's domestic politics ahead of a leadership transition next year.
"It was clear the civilian leadership was uninformed" of the J-20 test, said a senior U.S. defense official after the meeting between Mr. Gates and Mr. Hu.
Mr. Hu, who is due to step down as party chief in 2012, eventually confirmed to Mr. Gates that the test had taken place and assured him that it was pre-planned and not directed at the U.S., according to the American officials.
Mr. Gates said he accepted Mr. Hu's explanation about the J-20 test flight, but added that he had long-running concerns about civilian control over the Chinese military.
"I have had concerns about this over time," he said. "And frankly, that is one of the reasons I attach importance to a dialogue between the two sides that includes both civilian and military."
Citing diplomatic protocol, the U.S. officials declined to make public further details about how exactly Mr. Hu was informed about the test during the meeting. But television footage showed several uniformed Chinese generals and other senior officers in the room.
China's Foreign Ministry declined to comment on the U.S. account of the meeting. But analysts said that if accurate, it suggested that Mr. Hu had to seek clarification from his own military officials in the middle of the meeting.
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The J-20, which has been conducting runway tests for the past several weeks, took off from an airstrip at the Chengdu Aircraft Design Institute just before 1 p.m. local time and flew for about 15 minutes, according to Chinese bloggers.
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Bloggers also posted video and still images of the sleek, dark-gray, twin-engine plane—which looks similar to the U.S. F-22, the world's only fully operational stealth fighter—taking off and in flight in slightly hazy skies over a built-up area surrounding the airfield.
Military aviation experts say the images suggest that China is making faster-than-expected progress in developing a potential rival to the F-22 and the Russian T-50 which made its first test flight last year.
They also say that the People's Liberation Army, or PLA, appears to have wanted the images made public as Internet censors, who routinely delete politically sensitive material, have allowed them to be circulated.
The episode undercut a core message that Mr. Gates brought to Beijing about the need for transparency and predictability to build trust between the militaries of the world's lone superpower and its rising Asian rival.
Analysts said it also appeared to be a sharp personal message to Mr. Gates, who took a controversial decision to scrap production of the F-22 stealth fighter in 2009, justifying the move partly by saying that China would not be able to produce a similar aircraft by 2020.
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Mr. Hu's apparent lack of information is likely to fuel international concern that he and the other eight civilians who make up the Party's Politburo Standing Committee—China's top decision-making body—are losing some of their control over the PLA.
"It suggests worrying levels of assertiveness and defiance of civilian leadership within the PLA," said Rory Medcalf, director of the International Security Program at the Lowy Institute for International Policy in Sydney.
"This revelation confirms that the PLA is willing to take provocative, assertive steps regardless of diplomatic priorities—perhaps even in deliberate opposition to them."
Civilian control of the military has been a central tenet of the Chinese Communist Party since even before it took control of China. "Our principle is that the party commands the gun, and the gun must never be allowed to command the party," Mao Zedong wrote in a 1938 essay.
That principle has held for most of time since the Communists won power in 1949—though in practice there was often little distinction between the party and military, since most of China's leaders had military experience from the civil war.
In recent years, the party has been run by civilians without military backgrounds who have maintained their authority over the military in part through generous annual increases to the defense budget.
But after two decades of rapid military modernization, many Western and Chinese analysts say some factions within the PLA are pushing a hard-line agenda, which is having increasing impact on decision making in Beijing, especially in the run-up to the party leadership change in 2012.
While opinions aren't uniform within the military, some analysts speculate that nationalist generals are now feeling their power, as they're courted by prospective members of the incoming ruling elite, and are using that as leverage to influence foreign policy.
That agenda was apparent in China's more forceful stance last year on territorial disputes in the East and South China seas, and in hawkish public statements from serving generals and other senior officers, which often pre-empted comments from the civilian leadership.
It is not the first time that gaps have appeared between the military and political hierarchies. A lack of communication was also highlighted on Jan. 11, 2007, when China shocked the world by shooting down a disused satellite with a missile—and the Foreign Ministry appeared not to have been informed.
Later that year, the U.S. aircraft carrier Kitty Hawk was temporarily denied permission for a long-planned port call in Hong Kong—apparently again without the Foreign Ministry's awareness—an incident that Mr. Gates said afterward also suggested a "disconnect" between the military and civilian sides of the Chinese government.
Over the past week, the Foreign Ministry has appeared out of the loop again, repeatedly sidestepping questions about the J-20 images. It did so again Tuesday in a regular briefing from spokesman Hong Lei.
"As technology develops, and in accordance with the needs of national defense, it is natural for countries to upgrade their weapons equipment," he said.
"The development of China's weapons equipment is completely based on the needs of its own security, and it is meant to protect China's sovereignty, security and territorial integrity. It is not aimed at any country or specific target."
Mr. Gates arrived in Beijing Sunday on a three-day mission to deepen and stabilize military exchanges that China has repeatedly suspended for political reasons, most recently in January 2010 over U.S. arms sales to Taiwan.
However, China's military appears to be doing the bare minimum to revive military ties and ensure Mr. Hu's visit goes smoothly, while at the same time showcasing its growing firepower before a domestic and international audience, analysts say.
On Monday, Mr. Gates's Chinese counterpart, Gen. Liang Guanglie, rebuffed a U.S. proposal for a clear timetable of deeper strategic defense talks, and made clear that China would suspend military ties again if the U.S. sold more arms to Taiwan.
Mr. Gates said Tuesday that Chinese officials asked for more details on the agenda of the talks and that U.S. officials were drafting more concrete plans on the dialogue. "They are taking the proposal seriously," he said.
Pentagon officials said Mr. Gates was greeted enthusiastically by Mr. Hu and Yang Jiechi, the foreign minister, Tuesday and that the civilian leadership seems warmer to U.S. calls for an in-depth strategic dialogue.
But the more positive tone of Tuesday's meetings was soon eclipsed by the test flight, which aviation experts say showed that China had now moved on to testing the J-20's flight control software, its engines, and its aerodynamics.
But The Wall Street Journal did reach a waitress in the 365 Recreation Tea Shop, next to the airfield, who said several workers from the Institute were playing cards there.
"Did you guys see the test fight today, did it actually take off?" she was heard asking the customers, who were heard replying: "Yes, it took off and flew!" They declined to speak directly on the telephone with a reporter.
