U.S. President Barack Obama and Chinese President Hu Jintao vowed on Wednesday to work to find common ground as the two countries announced $45 billion (28 billion pounds) in export deals.

After a year of strains, the leaders of the world's only superpower and its fastest-rising rival opened a Washington summit that put the focus on often diverging agendas on currencies, trade, global security and human rights.

Welcoming Hu to the White House amid the pomp of a formal state visit, Obama hailed the event as a chance to demonstrate that we have an enormous stake in each other's success.

Seeking to show the benefits of economic ties, the two countries reached agreement on export deals worth $45 billion, including China's purchase of 200 Boeing aircraft, a senior U.S. official said shortly after talks began.

Even as our nations compete in some areas, we can cooperate in others, Obama said. Let us seize these possibilities together.

Gently raising China's human rights record, he said: History shows that societies are more harmonious, nations are successful and the world is more just when the rights and responsibilities of all nations and all people are upheld, including the universal rights of every human being.

Hu said he had come to enhance mutual trust and open a new chapter in relations but signalled he would bristle at any effort to push China on its currency practices, human rights and other disputes that it deems to be domestic matters.

China and the United States must respect each other's choices in development and each other's choices in development paths and each other's core interests, Hu said.

Hu was greeted with a 21-gun salute, honour guards and the playing of both national anthems, a carefully choreographed ceremony meant to convey recognition of China's growing international stature.

But while handshakes and smiles set a positive tone, the red-carpet treatment was not expected to make it any easier to achieve breakthroughs in Wednesday's talks or even narrow differences significantly.

Some in Washington and Beijing are treating the summit as a gauge of how well the two powers can work in concert as China's ambitions expand in line with its rapid economic growth.

U.S. Secretary of State Hillary Clinton called for more cooperation from China in dealing with North Korea's nuclear program and provocative behaviour. She also said the Obama administration was pressing Beijing very hard to gets its entities into compliance with U.N. sanctions on Iran.

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