US President Barack Obama has expressed his reservations about a contested Senate bill aimed at pressuring China to revalue its currency, saying it may not "actually work". Telling reporters in Washington on Thursday, Obama, who is facing a reelection bid in 2012 amid difficulties to create jobs for American voters, accused China of "gaming" trade by keeping its currency, the yuan, weak. However, Beijing has repeatedly said that it did not want to seek a deliberate huge trade surplus with the US. "China has been very aggressive in gaming the trading system to its advantage and to the disadvantage of other countries, particularly the United States," Obama told a news conference focused on his bid to revive a weak US economy. "Obviously we’ve been seeing a remarkable transformation of China over the last two decades, and it’s helped to lift millions of people out of poverty in China. We have stabilized our relationship with China in a healthy way. But what is also true is that China has been very aggressive in gaming the trading system to its advantage and to the disadvantage of other countries, particularly the United States. And I have said that publicly, but I''ve also said it privately to Chinese leaders. And currency manipulation is one example of it, or at least intervening in the currency markets in ways that have led their currency to be valued lower than the market would normally dictate. And that makes their exports cheaper, and that makes our exports to them more expensive. So we’ve seen some improvement, some slight appreciation over the last year, but it''s not enough." Now, the legislation that is being presented in Congress is an effort to get at that, Obama said. "My main concern -- and I’ve expressed this to Senator Schumer -- is whatever tools we put in place, let''s make sure that these are tools that can actually work, that they''re consistent with our international treaties and obligations. I don’t want a situation where we''re just passing laws that are symbolic knowing that they’re probably not going to be upheld by the World Trade Organization, for example, and then suddenly U.S. companies are subject to a whole bunch of sanctions. We''ve got a -- I think we''ve got a strong case to make, but we’ve just got to make sure that we do it in a way that''s going to be effective."