The dollar slid to its weakest point since late September on Tuesday even as Treasury Secretary Timothy F. Geithner, in Beijing, tried to reassure the Chinese government that its investments in $1 trillion of United States debt were secure.

But in the currency markets, investors who flocked to the safety of the dollar at the height of the financial crisis are beginning to shun the currency on concerns over inflation and the prospect of big buyers of United States debt losing their taste for Treasury notes.

The United States dollar index, which measures the dollar against other heavily traded currencies, fell to 78.41. One euro was worth about $1.43  its strongest position against the dollar since December.

Recent statements by Chinese officials have heightened fears that China will scale back its purchases of Treasury notes, which could make it more expensive for the United States to raise money.