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That would allow the Fed to avoid making the kind of upfront commitment to buy government debt on a large scale in the trillion-dollar range. It also could ease concerns among some Fed officials about carrying out the type of large-scale interventions seen during the recession.

The Fed ended up buying a total of roughly $1.7 trillion of mortgage securities and debt, as well as government bonds, during the recession.

Another big buying binge would complicate the Fed’s efforts later on to unwind all its stimuli. There are also concerns that another large-scale effort could spark inflation later on or trigger a wave of speculative buying that could create bubbles in the prices of bonds or commodities or other assets.

On Wednesday, the three Fed presidents in their speeches weighed the pros and cons of buying government debt in general, rather than the specific Bullard proposal.

Mr. Rosengren is a voting member of the Federal Open Market Committee, the group, including Fed Chairman Ben S. Bernanke, that makes decisions on interest rates and other policies that influence economic activity. Mr. Kocherlakota and Mr. Plosser both will be voting members next year, although they participate in the Fed meetings and debates over policy moves.

Mr. Kocherlakota spoke in London, while Mr. Plosser spoke in New Jersey.