The once-insular nation is broadening its international interests and investing around the globe, and its military is rapidly modernizing. So there is concern that U.S. and Chinese forces may find themselves bumping into each other without formal mechanisms in place for the two militaries to iron out disagreements.  Even as those worries grow, a longtime issue for China remains: It does not want the United States to sell weapons to Taiwan, which it still claims as part of its territory, and views that as the baseline of any talks. "The military relationship is a red-meat issue in China," said a senior Chinese diplomat, speaking on the condition of anonymity because of the sensitivity of the matter. "It is the one issue that could jeopardize our relations with the United States."  White House officials hope to diffuse that concern, arguing that the bigger matters between the two countries are more pressing than ever. Even at the height of the Cold War, senior administration officials have noted, the Pentagon had a more substantive relationship with the Soviet Union's military than it does with the People's Liberation Army today.  "China is reemerging as a great power," said Michael Schiffer, deputy assistant secretary of defense for East Asia. "Our militaries are coming into increasing proximity and increasing interactions. But we don't have any good mechanism to help us clarify misunderstandings."  The Obama administration got a taste of such a "misunderstanding" just two months into office. In early March, the U.S. Navy reconnaissance ship Impeccable was in the South China Sea hunting for Chinese submarines when it was swarmed by Chinese vessels that tried to block it and destroy its sonar equipment. A similar incident occurred in May in the Yellow Sea.  Both confrontations ended peacefully when the U.S. ships made it clear that they would leave; but the incidents highlighted "the risk," a senior Pentagon official said recently, "of having the entire bilateral relationship unravel based on the decision-making of 18-year-old seamen."  In the past, some U.S. officials said forging ties with the Chinese military wasn't that important. Even though its defense spending had risen dramatically, outpaced only by the United States', China's intentions were limited to defending its sovereignty.  But two developments have changed American thinking, analysts say. The first was the realization that every crisis between the United States and China -- including the Chinese army crackdown on Tiananmen Square demonstrators in 1989 and the accidental bombing of China's embassy in Yugoslavia in 1999 by U.S. planes -- has involved the nations' militaries.  The second was the conclusion that the People's Liberation Army wants to expand its activities around the world as China expands its international investments. Last year, China dispatched three navy ships outside of Asia for the first time in its modern history, sending them to fight piracy off Somalia alongside an international task force.  The Obama administration has held a series of high-level contacts with the Chinese army that will culminate with a visit to the United States this month by Xu Caihou, a vice chairman of the Central Military Commission and the highest-ranking Chinese military official to come here in years.  But beyond that, China's military seems intent on keeping the Pentagon at arm's length, and U.S. officials point to number of concerns.  The Chinese have built up their conventional missile forces to such an extent that a Rand Corp. report concluded in August that an attack could "cut every runway at Taiwan's half-dozen main fighter bases and destroy essentially all of the aircraft parked on ramps," allowing China total domination of the skies above Taiwan. But this strategic shift has not been accompanied by significant talks between China and the United States, which is legally bound to provide for Taiwan's defense.  The Pentagon estimates that by next year, China will deploy as many as five Jin-class submarines, each with a capacity of 12 nuclear-armed intercontinental ballistic missiles. But there is no protocol for how the American and Chinese navies should deal with incidents at sea.  China also has shown little interest in a dialogue about nuclear strategy. It now deploys mobile, solid-fuel intercontinental ballistic missiles and has more than doubled, to about 80, its supply of nuclear-armed medium-range ballistic missiles. Except for one round of talks with the Bush administration, it has shared no information on its nuclear plans.  Three years ago Washington invited the head of China's nuclear weapons command to the United States, but he has yet to come.  China knocked an old satellite out of the sky in 2007 when it tested an anti-satellite weapon, and a recent space launch came within 100 miles of the international space station. But Beijing has not talked to the United States about how to deal with the debris or how its space program, run by the army, should interact with those of other nations.  China also is believed to be working on a new fighter jet. But it has not hashed out a protocol for what to do when its airmen encounter the American military in the skies. In 2001, a Chinese fighter bumped into a U.S. Navy reconnaissance plane over Hainan Island. The fighter pilot was never found, and the Americans crash-landed on Chinese territory, sparking an 11-day standoff before the Chinese released the crew.  And while U.S. and Chinese diplomats have coordinated their strategies to confront North Korea's nuclear program, the Chinese military has rejected the Pentagon's request to discuss contingencies if the North Korean government collapses.  When Undersecretary of Defense for Policy MichÃ¨le Flournoy visited China in June, officials there gave her a list of what they called seven "obstacles" that needed to be removed if ties were going to improve, according to several American and Chinese officials and analysts. The Chinese said they wanted U.S. reconnaissance vessels out of their 200-mile exclusive economic zone, bristled at the fingerprinting of senior Chinese military officers when they entered the United States and objected to being a target of U.S. nuclear weapons.  But at the top of the list was a demand that the United States stop selling weapons to Taiwan.  Three times over the past three years, Taiwan has asked to buy dozens of new F-16 fighter jets from the United States, and each time Washington put the request off, fearful of alienating China. After his trip, Obama has to decide whether to sell Black Hawk helicopters and Patriot anti-missile batteries to Taiwan, and soon after that, he must decide whether to sell 66 F-16s. The United States last sold F-16s to Taiwan in 1992.  "Selling the F-16s to Taiwan would be a big, big problem for us," said the senior Chinese diplomat. "Cooperation on other things would naturally be affected."
During his first visit to China next month, President Obama hopes to strengthen ties with Beijing on efforts to combat climate change, address the global financial crisis and contain nuclear proliferation in North Korea and Iran. Perhaps most important, he also aims to improve the U.S. relationsh...