WASHINGTON – The two biggest foreign buyers of U.S. Treasury securities kept investing during a tense fight in Washington over raising the government’s borrowing limit. But overall foreign holdings fell in July for only the second time in more than two years, a sign that some investors worried about a possible default.

The Treasury Department’s monthly report issued Friday showed that China, the biggest buyer of U.S. Treasury debt, increased its investments for a fourth straight month. Japan, the second-largest buyer, also invested more.

But total holdings dipped 0.4 percent to $4.48 trillion in July, the second decline since April 2009. Russia, India and the Caribbean banking centers, which include the Bahamas and Bermuda, all trimmed their holdings.

Congress and the Obama administration reached a deal on Aug. 2 to increase the nation’s borrowing limit by more than $2 trillion. The agreement was approved just hours before a potential default.

Net purchases of long-term securities, a category that includes not only U.S. government debt but also bonds sold by U.S. corporations, rose $9.5 billion in July.

But Caribbean banking centers cut their holdings 12.1 percent to $124.5 billion and Russia slashed its investments 8.7 percent to $100.2 billion.