China's currency strengthened on Friday to its highest level against the U.S. dollar since its July 21 revaluation on high market expectations and ahead of a planned visit by Chinese President Hu Jintao to Washington.

The Shanghai-based China Foreign Exchange Trade System reported the daily benchmark, or the central parity rate for the dollar stood at 8.0170 yuan, falling for the first time below 8.02 yuan, a new low over the past 12 years.

The Chinese currency, also known as renminbi or RMB, chalked up the biggest weekly appreciation from last Monday to Friday, and gained more than 3 percent since the July yuan reform.

The market welcomed the news that President Hu Jintao is due to visit the United States and that China's foreign exchange reserves had ballooned up to be the biggest of any country, said Cao Honghui, a finance research fellow with the Chinese Academy of Social Sciences, a high-profile government think-tank.

Hu will pay a state visit to the United States in mid or late April, a trip a Foreign Ministry spokesman said is aimed at enhancing mutual trust and expanding common understanding.

China raised the value of yuan by 2 percent and scrapped its decade-old peg to the U.S. dollar, instead of linking it to a basket of currencies and allowing it to float up or down within a limited range.

But the United States said the rise is too small. American manufactures contend that RMB was undervalued by as much as 40 percent, giving Chinese exporters an "unfair" price advantage and hurting the U.S. labor market.

The U.S. pressure on China's currency issue built up as China's trade surplus with the United States hit a new high in 2005. Statistics provided by China and the United States differ significantly. China said the Sino-U.S. trade hit 212 billion U.S. dollars last year.

Two U.S. senators have said they would delay for six months a vote on a bill punishing China for "restricting its exchange rate, " saying they had seen "signs of currency reform" during a recent trip to China.

The bill, sponsored by Republican Senator Lindsey Graham and Democratic Senator Charles Schumer, would impose 27.5 percent tariffs on Chinese imports if the currency dispute is not settled. The lawmakers said if the pace of China's currency reform slowed, they would call for a vote.

The media reported little about the currency topic during a visit by U.S. Commerce Secretary Carlos Gutierrez to Beijing on the heels of the two senators.

Chinese Vice Premier Wu Yi will leave Beijing on Monday for Washington to co-chair the 17th meeting of the Sino-U.S. Joint Commission on Commerce and Trade with Gutierrez and U.S. Trade Representative Rob Portman. The two sides will discuss their respective concerns, China's Foreign Ministry has said.

China's foreign currency reserves are boosted as the country buys dollars and other foreign currencies that come into the economy, amid booming foreign trade, and stockpiles them in U.S. Treasury bonds and other assets -- as a means of foreign exchange controls and to guard against possible inflation, analysts say.

The China Business News has reported, citing unnamed sources, the nation's foreign currency reserves reached 853.7 billion U.S. dollars by the end of February, likely topping Japan's to become the world's largest. Government figures were only released on a quarterly basis.

Central banker Zhou Xiaochuan, however, has said it is "not reliable" to achieve Sino-U.S. trade balance only through adjusting exchange rates.

Li Chao, a spokesman for the People's Bank of China (PBoC), or the country's central bank, also contended last week that the skewed trade with the United States was an outcome of a high savings rate in China as against an extremely low one in the United States. In theory, excess savings produce trade surpluses, and vice-versa, savings shortfall means deficits, he acknowledged.

China will not have another one-off revaluation of yuan, he said,echoing an earlier claim by Premier Wen Jiabao.

The PBoC early this year began a new policy of calculating the yuan's benchmark value against the U.S. dollar using a weighted average of the prices given by major banks. The highest and lowest offers are excluded from the calculation.

Giving banks a role in setting the daily exchange rate is seen as a sign that the central bank is willing to allow market forces a greater role in daily trading, analysts acknowledge.

But the yuan is allowed to move 0.3 percent up or down from the benchmark value against the dollar per day. "Only propelled by new market factors can the floating band be enlarged," said director Xia Bin with the finance research institute of the State Council Development Research Center.