President Barack Obama has taken a big step to broaden the US relationship with China with the launch of a new dialogue, but some experts warn more symbolism than substance could be at play.

The new US leader, visiting London for the Group of 20 summit on the global economic crisis, met with Chinese President Hu Jintao and agreed to "strengthen ties at all levels."

The world's most powerful and most populous nations agreed that US Secretary of State Hillary Clinton and Treasury Secretary Tim Geithner would meet once a year for talks with senior Chinese officials Dai Bingguo and Wang Qishan.

Clinton's deputy Jim Steinberg said the United States hoped to work with China on everything from climate change to dealing with Iran, Sudan and Zimbabwe.

"On these and other issues, China must be part of the solution," Steinberg told the National Bureau of Asian Research, a think-tank.

"US-China relations are now at a jumping off point and faced with an important development opportunity," Hu was quoted as saying by The People's Daily, the main mouthpiece of China's ruling Communist Party.

"The two sides can and should work jointly to build comprehensive, positive and cooperative ties for the 21st century."

During what a US official characterized as a "business-like" meeting between Hu and Obama, the leaders also vowed to expand consultations on "non-proliferation and other international security topics." And Obama accepted Hu's invitation to visit China in the second half of the year.

Under the new mechanism, Washington and Beijing have appointed two officials responsible for the strategic dialogue and the economic dialogue, respectively, foreign ministry spokesman Qin Gang told reporters in Beijing.

"The importance of the cooperation is greater than in the past," he said.

Business leaders welcomed the new US-China dialogue.

US Chamber of Commerce chief Thomas Donahue said it would be "a critical forum to forge common solutions that can return the global economy to prosperity and address shared geopolitical challenges."

But Derek Scissors, a China expert at the conservative Heritage Foundation, said that was wishful thinking.

"Until and unless this mechanism yields results, it will be another venue for empty talk," Scissors said.

He doubted that a partnership would impact the economic crisis, saying that China was unfairly maintaining a huge trade surplus rather than working with the United States.

"The partnership is not strengthening, but weakening," he said.

World Bank president Robert Zoellick has argued that the Group of 20 major industrialized and developing nations hinged on action by the "G2" -- the United States and China.

Writing in The Washington Post last month with World Bank chief economist Justin Yifu Lin, Zoellick said that "these two economic powerhouses must cooperate and become the engine for the Group of 20."

Such talk riles many policymakers in Japan, the world's second largest economy and a close US ally that has historically had tense ties with China.

Japan relishes its role as the only Asian member of the Group of Eight major industrial powers.

Ralph Cossa, head of the Pacific Forum of the Center for Strategic and International Studies, cautioned against elevating the US-China dialogue into anything akin to a G2.

"No problem can be solved without the US and China cooperating, but it takes more than just the two of them. You certainly can't ignore the second largest economy, or the EU," he said.

But Cossa said the new dialogue could allow the United States and China to tackle global issues and quietly discuss human rights -- including US concerns about Beijing's treatment of Tibet.

He noted that the scope of US-China talks has significantly expanded beyond the usual US concerns of trade, human rights and Taiwan.

"Now, when we sit down the first thing we talk about is Iran, the global financial crisis, climate change or what's happening in Latin America, Africa, Burma and North Korea," he said.