WASHINGTON — The Federal Reserve Board will not meet its upcoming April 21 deadline to issue final rules that would limit interchange fees for debit cards.

In a letter to House Financial Services Committee Chairman Rep. Spencer Bachus, Fed Chairman Ben Bernanke said the central bank required more time to review the more than 11,000 comment letters it has received on its proposal issued in December.

"Because of the volume of comments and the complexity of the issues raised in those comments, however, we have concluded that we will be unable to meet the Act's directive that the Board issue final interchange fee standards by April 21," Bernanke wrote in his letter.

The Fed's proposal would limit interchange fees on debit cards to 12 cents. Bankers have argued the cap is too low and ignores several costs of running a debit system, including fraud prevention.

Many of the letters, Bernanke said, were "quite detailed and extensive" and reflected the importance of the issue given that debit transactions have grown significantly over the past decade.

"We believe the information provided in these comments is important for assessing fully the effect of the proposed rule on the U.S. payments system and its users and providers," he wrote.

Despite missing its deadline, provisions included in Dodd-Frank on interchange would still go into effect on July 21 even without a final rule. But Bernanke said the Fed would finish its work ahead of the deadline.

"We are committed to completing the rulemaking for that provision in advance of that date," Bernanke wrote.