Those Fed officials argued that the pledge won't stop the Fed from boosting rates if the economy showed signs of picking up substantially or if inflation took off. On the other hand, the pledge "could last for some time" if the economy took a turn for the worse.
To aid the recovery, the Fed at its March 16 meeting held its target range for its bank lending rate at zero to 0.25 percent. It's stood at that level since December 2008. And it maintained a pledge -- in place for a year -- to keep rates at rock-bottom levels.
Thomas Hoenig, president of the Federal Reserve Bank of Kansas City, for a second straight meeting was the sole opponent in keeping the pledge.
Hoenig worries that low rates could cause a buildup of "financial imbalances" and put the economy's stability at risk. Analysts saw Hoenig as concerned that holding rates too low for too long could feed some new speculative bubble in assets such as stocks or commodities.
Fed members noted the importance of closely monitoring financial markets and institutions to help detect risks at an early stage. They cited, in particular, the need to monitor asset prices and loan levels.
Information collected by Fed staff hasn't revealed significant threats in the financial markets or widespread high-risk-taking, the minutes concluded. Still, Fed officials said they would be on the watch for any such threats.
A major challenge for the Fed is deciding when to boost rates. Moving too soon could hurt the recovery. But waiting too long could unleash inflation.
Hoenig favored dropping the "extended period" pledge. He would replace it with language saying economic conditions warrant low rates for "some time." Hoenig suggested such a change would give the Fed flexibility to begin raising rates modestly when the time was right, the minutes explained.
Hoenig said he believed the Fed would need to start boosting rates "sooner rather than later."
The Fed has leeway to hold rates low because inflation isn't a threat. Most Fed officials believed substantial "slack" in the economy would continue to tamp down inflation pressures, the minutes said.
By slack, Fed officials mean the fact that factories and other businesses are still operating below full throttle and that the job market -- while improving -- remains weak. Workers won't be able to negotiate sizable pay raises or other compensation any time soon.
Companies will be hard-pressed to ratchet up retail prices when shoppers are reluctant to go on spending sprees. All those forces should keep inflation in check.