The Federal Reserve was unsure last month whether lower borrowing costs were needed to cushion the US economy from a housing slump and credit woes but decided to cut interest rates as a form of insurance.
"Many members noted that this policy decision was a close call," minutes of the Fed's October 30th-31st meeting released day said.
The minutes were in keeping with recent comments from Fed officials suggesting rates were low enough to see the economy through a slow-growth period.
However, they also showed policy-makers believed the economy still faced large risks and failed to dissuade financial markets from betting rates would drop further.
"Most members saw substantial downside risks to the economic outlook and judged that a rate reduction at this meeting would provide valuable additional insurance against an unexpectedly severe weakening in economy activity," the minutes said.
In addition to the minutes, the US central bank took a step toward pulling back its veil of secrecy and issued updated forecasts that showed officials expect a much more sluggish economy next year compared to forecasts before financial turmoil hit in the summer.
The Fed projected US economic growth to slow in 2008 to between 1.8 per cent and 2.5 per cent,
sharply down from the 2.5 per cent to 2.75 per cent forecast in June, before picking back up in 2009.