It reflects both election-year politics over a loss of American jobs and great frustration over unfulfilled promises by China to allow its currency to rise in value, which would make Chinese goods less competitive in the United States.

The Obama administration never took an emphatic position on the legislation and some officials say that, if passed, signed into law and challenged at the World Trade Organization, it might well be struck down. But this is a case where the symbolism may be more important than the legal niceties, and for that reason, the White House has been of two minds about the bill.

Mr. Obama has tried to use the rising public anger over China’s trade advantage to argue to Chinese leaders that the United States would no longer tolerate deliberate currency manipulation, a point Mr. Obama made repeatedly in a meeting last week with Wen Jiabao, China’s prime minister. He did so again on Wednesday in Des Moines, where one businessman asked the president about the issue.

“The reason that I’m pushing China about their currency is because their currency is undervalued,” he said, adding: “People generally think that they are managing their currency in ways that make our goods more expensive to sell and their goods cheaper to sell here. And that contributes — that’s not the main reason for our trade imbalance — but it’s a contributing factor to our trade imbalance.”

But in conversations with Congress, the Treasury secretary, Timothy F. Geithner, and other officials have warned of the danger of touching off a trade war, in which China blocks American goods in retaliation, that could hurt both economies.