HONG KONG  Leaders in both Washington and Beijing have been fretting openly about the mutual dependence  some would say codependence  created by China’s vast holdings of United States bonds. But beyond the talk, the relationship is already changing with surprising speed.

China is growing more picky about which American debt it is willing to finance, and is changing laws to make it easier for Chinese companies to invest abroad the billions of dollars they take in each year by exporting to America. For its part, the United States is becoming relatively less dependent on Chinese financing.

China has actually bought Treasury bonds at an accelerating pace over the last year  notwithstanding Chinese officials’ complaints about American profligacy. But the borrowing needs of the United States government have grown even faster. So China represents a rapidly shrinking share of overall purchases of Treasury securities. “China’s demand for Treasuries has increased over the past year, but it hasn’t increased at anything like the pace of the Treasury’s sale of new Treasury bonds,” said Brad W. Setser, a specialist in Chinese financial flows at the Council on Foreign Relations.

Americans and investors elsewhere are buying Treasuries instead. They are saving more and have been shifting out of other investments  including equities until the past two months  and into Treasuries.