More broadly, the report described an ambitious Chinese military program aimed at transforming the People’s Liberation Army into a modern force, fueled by years of double-digit increases in defense spending. Its main goals include preserving Communist Party rule and preparing for possible hostilities in the Taiwan Strait, the report said.

China and Taiwan split amid civil war in 1949. Despite a marked improvement in relations over the past four years, China still threatens to attack across the Taiwan Strait if Taiwan moves to make its de facto independence permanent. U.S. arms sales to Taiwan are a frequent source of diplomatic friction with Beijing.

“China’s military shows no sign of slowing its efforts to prepare for Taiwan Strait contingencies,” David Helvey, the acting deputy assistant secretary of defense for East Asia, told a Pentagon news conference.

Beyond that, China has been developing a capability to project power well beyond its shores. One element of that is its expansion of naval power, including an anti-ship ballistic missile seen as a potential threat to U.S. aircraft carriers. Last year China also launched sea trials of its first carrier, a refurbished hulk purchased from Ukraine. Friday’s report said China also may have begun work on its first built-from-scratch carrier.

The report, which in past years has drawn critical reviews in Beijing, was shorter than earlier versions and struck a measured tone. The Pentagon said it was meant to present data in a “descriptive, analytical manner.”

China’s military buildup is a central focus of the Obama administration as it shifts its attention more toward Asia and the Pacific in the aftermath of fighting wars in the greater Middle East over the past decade. The U.S. is not building new permanent bases in Asia but is seeking more security partnerships in the region.

Last year’s Pentagon report forecast the possibility of China beginning construction of a fully indigenous carrier; this year’s version went slightly farther, saying “some components” of the first carrier may already be under construction. It said that carrier could be ready for use after 2015, and that China is likely to build more of them.

“It will still take several additional years for China to achieve a minimal level of combat capability for its aircraft carriers,” the report said, because it does not yet have pilots fully trained in carrier flight operations.

The Pentagon also said China’s military is pursuing “new historic missions” that go beyond its traditional role of defending the homeland. These additional missions include humanitarian aid, combating piracy in the Gulf of Aden and counter-terrorism operations. The Pentagon cited as an example China’s evacuation last year of 36,000 Chinese nationals from Libya during the uprising against Moammar Gadhafi.

Helvey said these Chinese operations abroad offer chances for cooperation with the U.S. military, which also has an interest in combating piracy and terrorism. On the other hand, he said, the U.S. will be watching closely to see that as it extends its reach around the world China lives up to its obligation to “uphold international norms and rules and to support the international community’s interests in peace and stability.”

Defense Secretary Leon Panetta is expected to make his first visit to China as Pentagon chief as early as this summer. On May 7 he hosted his Chinese counterpart, Gen. Liang Guanglie, in Washington.

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Robert Burns can be followed on Twitter at http://twitter.com/robertburnsAP

The Air Force grounded its F-22s for four months last year because of the oxygen-deficit problem, and now some pilots are refusing to fly them. An Air Force advisory panel headed by a retired Air Force general studied the problem for seven months and reported in March that it could not pinpoint the root cause. It endorsed a plan keeping the aircraft flying, however, with pilots using special sensors, filters and other safety precautions.

Panetta was briefed on the problem last Friday, just days after a CBS “60 Minutes” report featured two F-22 pilots who said that during some flights they and other pilots have experienced oxygen deprivation, disorientation and other problems. They cited safety concerns as well as the potential for long-term personal health issues.

Asked why Panetta was acting now, Navy Capt. John Kirby, a Pentagon spokesman, said the defense chief has been aware of the F-22 problem “for quite some time.” In light of the recent deployment of several F-22s to the Persian Gulf and because of pilots’ expressions of alarm, Panetta chose to “dive a little more deeply into the issue.”

In a letter to Air Force Secretary Michael Donley, Panetta ordered that F-22 flights remain “within proximity of potential landing locations” so that pilots can land quickly in the event they experience an oxygen-deficit problem. Kirby said the specifics of those flight restrictions are to be set by individual F-22 pilots and commanders.

Panetta also told Donley to accelerate the installation of an automatic backup oxygen system in each F-22. The first of those is to be ready for use by December, Kirby said.

And the Pentagon chief ordered the Air Force to call on the expertise of the Navy and NASA in pursuit of a solution.

Panetta’s actions have no immediate effect on U.S. combat operations, since the F-22 is not operating in Afghanistan. But Panetta said the plane would give up long-distance air patrol missions in Alaska until the planes have an automatic backup oxygen system installed or until Panetta agrees the F-22 can resume those flights. Other aircraft will perform those missions in the meantime.

Panetta’s chief spokesman, George Little, told reporters that Panetta supports the Air Force’s efforts to get to the bottom of the problem.

“However, the safety of our pilots remains his first and foremost concern,” Little said.

The F-22 Raptor, which has never flown in combat, recently deployed to the United Arab Emirates for what the Pentagon called routine partnering with a Middle East ally. Little, the spokesman, told reporters that Panetta’s order to impose new flight restrictions would not affect flight operations during the UAE deployment.

The plane, conceived during the Cold War as a leap-ahead technology that could penetrate the most advanced air defenses, is seen by some as an overly expensive luxury not critical to fighting current conflicts. The fleet of 187 F-22s — the last of which was fielded just two weeks ago — cost an average of $190 million each.

Panetta’s predecessor as Pentagon chief, Robert Gates, persuaded Congress to cap production of the F-22 earlier than originally planned. He saw it as primarily of use against a “near-peer” military competitor like China, noting that the plane did not fly a single combat mission during a decade of war in Iraq and Afghanistan.

With its stealth design, the F-22 is built to evade radar and has advanced engines that allow it to fly at faster-than-sound speeds without using afterburners. It manufacturer, Lockheed Martin, describes the plane as “the only fighter capable of simultaneously conducting air-to-air and air-to-ground combat missions with near impunity.”

The fleet of 170 F-22s is stationed at six U.S. bases: Joint Base Elmendorf-Richardson, Alaska: Joint Base Pearl Harbor-Hickam, Hawaii; Joint Base Langley-Eustis, Va.; Nellis Air Force Base, Nev.; Holloman Air Force Base, N.M.; and Tyndall Air Force Base, Fla.

F-22 pilots are trained at Tyndall. Flight testing is at Edwards Air force Base, Calif., and operational testing and tactics development is performed at Nellis.

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Robert Burns can be followed on Twitter at http://twitter.com/robertburnsAP