BEIJING -- The United States wants to expand investment in China via more open markets and wider access, a US trade official said Thursday.

Franklin Lavin, undersecretary of commerce for international trade, said there is significant potential for companies to invest in fast-growing China, which needs investment.

"China needs private investment so that its high-performing companies can move up to the international level," Lavin said, noting that the Chinese government would have to face up to this challenge over the next ten years, and that international management and investment could help to speed up the transformation.

Highlighting efforts by Beijing to keep its World Trade Organization commitments, Lavin acknowledged that trade frictions and barriers still exist in bilateral relations, and called on the Chinese government to open the domestic market wider and deeper for international investment.

China's trade surplus with the United States exceeded US$140 billion last year, sparking a strong response from the US Congress and media.

Two senators were reportedly planning tough legislation that would push China to change its currency policies, which critics say have contributed to the trade imbalance and job losses in the United States.

"The relationship between the US and China might be the single most important bilateral relationship in the world," Lavin said, noting that senior-level commitments from both sides can help to move problems towards solutions.

"I am generally optimistic," Lavin said.