AMERICAN inflation, which has seemed to some conservative economists to be an impending threat ever since the Federal Reserve began to buy large quantities of government securities, appears to be falling to levels lower than any seen in recent years. There are similar declines in many European countries.

The decline in the inflation measure most watched by the Federal Reserve — the personal consumption expenditures deflator — could provide a reason for the Fed to delay the widely expected tapering of bond purchases. Last week, the government reported that the price index had risen only 0.9 percent over the 12 months through September. “Fed officials have said that their ultra-easy monetary policy is justified not only by weakness in the labor markets but also by declining consumer price inflation, especially if it gets too close to deflation,” Ed Yardeni, the chief investment strategist of Yardeni Research, wrote this week. “They’ve indicated that even if the unemployment rate falls down to 6.5 percent, they might be in no rush to tighten policy if inflation remains too low.”

The unemployment rate in October was 7.3 percent, and the Fed had not been expecting the personal consumption expenditures inflation rate to fall as low as it has.

Inflation has also been falling in Europe, where the European Central Bank cut interest rates last week in response to a surprising estimate that consumer prices in the euro zone rose just 0.7 percent in the year through July.