The Bank of Japan may have fired the first shot in a new round of central bank action to prop up the global economy as recoveries in industrial nations falter. The unexpected decision by the Japanese central bank yesterday to drop its interest rate to “virtually zero” and expand its balance sheet comes as Federal Reserve policy makers move toward more unconventional easing. Bank of England officials will consider further stimulus tomorrow, while the central banks of Australia, Canada and New Zealand are among those now holding fire on further interest-rate increases. The renewed push toward easier monetary policy comes as the International Monetary Fund warns growth in advanced economies is falling short of its forecasts ahead of its annual meetings in Washington this week. The dilemma for policy makers is that their actions may do little to revive growth and end up roiling currency markets.