U.S. Defense Secretary Robert Gates, who arrives late Sunday for a five-day visit, will formally restore military-to-military exchanges, cut off a year ago by Beijing over U.S. arms sales to Taiwan. His visit marks the first to China by a serving defense secretary since William Cohen's in 2000.

In the past year, China's diplomatic and military stance has became increasingly muscular, even confrontational, most notably at sea. Worried Asian neighbors turned to the United States, which was already stepping up its engagement with the region.

"We are settling into what all observers agree is a Sino-American security rivalry. The key is to manage and stabilize it so it does not become a conflict," said Dan Blumenthal, a former China country director at the Pentagon and a resident fellow at the American Enterprise Institute in Washington, D.C.

China says it's not a threat and its military is purely for defense — which in its definition includes deterring Taiwan, a self-governing island that Beijing claims as its territory, from declaring formal independence.

Chinese officials have been ratcheting down their rhetoric, partly to ensure a smooth visit by President Hu Jintao to Washington later this month. Military contacts with the United States quietly resumed in October, and the invitation to Gates is the strongest signal to date of a more conciliatory approach.

But China's growing military strength can be at odds with the government's avowed policy of a "peaceful rise" — that a more powerful China will not threaten its neighbors or upset the global order.

In an interview with America's Public Broadcasting Service that aired Thursday, Gates said the U.S. needed to be mindful of China's growing capabilities, but there was "no reason for China to be an adversary."

"So I think looking for ways to be constructive, to be more open, to better understand what each other's intentions are with some of these capabilities, this is the way that sovereign nations deal with each other," Gates said.

In an apparent nod to U.S. calls for more transparency, China conducted runway tests on Thursday and Friday of its prototype stealth fighter, the J-20, in the southwestern city of Chengdu.

While there was no official comment on the tests, still photos and video of the plane taxiing on the runway were widely distributed on the Chinese Internet — a sign of official approval since government censors routinely remove politically sensitive content.

"This is absolutely connected to Gates' visit. The leaders are saying 'you want us to be more transparent? We'll show you," said Andrei Chang, editor of Kanwa Asian Defense magazine and an expert on the Chinese military.

Chinese officers have said they want to field such a jet within eight to 10 years.

China's leaders are caught between the view that Beijing should take advantage of reduced American influence and increased Chinese power to press its foreign policy demands and fears that a more aggressive diplomacy is undoing 15 years of effort to promote China's rise as peaceful, said Rosemary Foot, a professor of international relations at Oxford University.

The army's role is somewhat unclear: While top generals appear publicly in lock step with the Communist Party leadership, lower-ranking and retired officers have increasingly voiced more bellicose views.

Gates will be anxious to find out whether the latter represents a genuine independent voice coming from the People's Liberation Army, which has 2.3 million troops.

"We will want to gain a sense of how much the PLA operates as an autonomous foreign policy actor and whether they view American weakness as an opportunity or as a threat to stability in the region," said Victor Cha, the former Asia chief at the National Security Council under President George W. Bush.

China sent navy vessels and military aircraft closer to Japanese territory last year than ever before. In April, Chinese ships were spotted in international waters off Okinawa, and a Chinese helicopter came within 300 feet (90 meters) of a Japanese military vessel monitoring a Chinese naval exercise.

In Southeast Asia, stronger Chinese assertions of territorial claims to disputed islands prompted a statement from U.S. Secretary of State Hillary Clinton that Washington considered the peaceful resolution of the disputes to be in the U.S. national interest.

Such statements and America's renewed commitment to Asia generally worry China, said Niu Jun, a professor at Peking University's School of International Relations. "China is very keen to find out why that is," he said.

China's assertive behavior magnifies the perceived threat from its growing defense spending. China announced a smaller-than-usual 7.5 percent increase to $76.3 billion last year — the second largest defense budget in the world behind the United States. Actual spending, including funding for new weapons and research and development, is believed to be as much as double that.

Bigger budgets fed by rapid economic growth have allowed China to speed up development of new technologies such as the J-20, which has yet to undertake an actual flight.

China is also moving toward launching its first aircraft carrier, though it will take years to learn how to operate it. China is overhauling an old Ukrainian carrier to use for training and is expected to begin work on a home-built carrier, according to the U.S. Office of Naval Intelligence.

A more immediate concern is the ongoing development of the DF-21D "carrier-killer" missile, one that could hold a U.S. aircraft carrier battle group at bay in any confrontation over Taiwan. The head of the U.S. Pacific Command, Adm. Robert Willard, told a Japanese newspaper last month that he believed the missile had achieved "initial operational capability," meaning China has a workable design that is undergoing further development.