China's Vice President Xi Jinping will Tuesday meet US President Barack Obama in a key early test for Washington's relations with the man on course to lead the Asian power for the next decade.

Xi will start a week-long visit with a welcome at the White House and talks with Obama and other top US officials, who are eager to get off to the right start with a leader whose views remain opaque.

The 58-year-old will later try to show a gentler side to the US public -- and perhaps also to television viewers in China -- when he tours the farm state of Iowa, where he paid a formative first US visit in 1985, and Los Angeles.

Xi, who arrived in Washington on Monday, is expected to succeed President Hu Jintao in 2013. Chinese presidents generally serve two five-year terms, meaning Xi could be in charge when some experts forecast that China will surpass the United States as the world's largest economy.

Despite the likely feel-good tone of Xi's tour, the United States and China have had an increasingly fractious relationship. White House officials have pledged to press Xi on concerns including the value of China's currency, which US lawmakers say is undervalued to boost its exports.

China has watched uneasily as the Obama administration steps up military ties with its neighbors including the Philippines and Vietnam, which have turned to the United States amid heated territorial disputes with Beijing.

In a written interview with The Washington Post, Xi said that he welcomed a "constructive" US role in East Asia's security but warned not to "deliberately give prominence to the military security agenda."

But in an unusual step, Xi will Tuesday visit the Pentagon and be welcomed with a full honor ceremony with music and cannons, weather permitting.

US officials have repeatedly sought greater defense cooperation with China, hoping to find out more about how it is spending its growing defense budget and also to reduce the potential for unintentional clashes.

"Our military posture in the Asia-Pacific region is not geared toward any one country. We have an arc of interest that stretches from Japan and Korea all the way down to Australia and across India," Pentagon spokesman George Little told reporters.

"We'll maintain a strong military presence in the region because of these varied interests and I'm sure that will be one of the topics discussed in the meeting with the vice president," Little said.

Tuesday amounts to a major day of diplomacy for China, with Premier Wen Jiabao holding a summit in Beijing with the European Union that is expected to touch on the Iranian nuclear row and escalating violence in Syria.

US officials who have met Xi generally describe him as more extroverted and spontaneous than the famously wooden Hu. Xi, by all accounts, had a favorable impression of the United States when he visited Iowa in 1985 and his daughter attends Harvard University.

But Xi's priorities remain a mystery to China watchers in the United States. Some experts believe he will have little room for maneuver unless he proves his authority on the Politburo's consensus-driven Standing Committee.

Xi has spoken little in public about the lessons from his father Xi Zhongxun, a noted communist revolutionary who fell out of favor with Chinese leader Mao Zedong and was subjected to one of his infamous political purges.

Human rights groups say that China has carried out a sweeping clampdown on dissent since last year, likely in fear of the influence of revolts that have overthrown authoritarian leaders in the Arab world.

Residents say China has also recently imposed virtual martial law in Tibetan areas after at least 19 Tibetans set themselves on fire to protest what they see as a lack of religious and political rights under Beijing's rule.

Flag-waving Tibetans marched through Washington to greet Xi. Four activists were briefly arrested on the Arlington Memorial Bridge, a major thoroughfare into Washington, for hanging up a banner that read: "Xi Jinping: Tibet Will be Free."

Lhadon Tethong, an activist with Students for a Free Tibet, said the group put up the banner to draw attention to the "all-out assault" in Tibet along with China's diplomatic support for Syrian President Bashar al-Assad.

"Xi Jinping is the last person that we believe President Obama should basically have a date with on Valentine's Day," she said.

"He represents everything counter to what Americans believe about human rights, freedom, democracy and dignity of people," she said.