Federal Reserve officials, taken aback by sharp criticism of their decision to print money and buy $600 billion in Treasury bonds, are counterpunching to defend themselves and, in some cases, to reinforce their commitment to the policy.

Charles Evans, president of the Federal Reserve Bank of Chicago and a strong supporter of the Fed's easing policy, noted in an interview with The Wall Street Journal that the weak economy and low inflation warranted the Fed's action and that more such purchases might be needed in months ahead if the economic outlook doesn't turn. "I would continue to want to apply accommodative monetary policy until I had some confidence that that situation was changing," Mr. Evans said, noting that $600 billion is a "good place to start" the easing program.

Eric Rosengren, president of the Federal Reserve Bank of Boston and another strong supporter of the easy-money policy, echoed those comments: "As long as the economic outlook doesn't improve dramatically I would expect that we will purchase the entire amount," he said, adding, "if the economy were to weaken and we were to get further disinflation and a higher unemployment rate, then we would have to reflect on whether we should take additional action." Disinflation is a decline in inflation.

Their comments came after top Fed officials, including Vice Chairwoman Janet Yellen and New York Fed President Bill Dudley, in earlier interviews with The Wall Street Journal, New York Times and CNBC, defended the Fed's policy as a needed step for the U.S. economy.