Washington ? The cascade of bank failures this year surpassed 100 on Friday, the most in nearly two decades. And the trouble in the banking system from bad loans and the recession goes even deeper than the number suggests.

Dozens, perhaps hundreds, of other banks remain open even though they are as weak as many that have been shuttered. Regulators are seizing banks slowly and selectively — partly to avoid inciting panic and partly because buyers for bad banks are hard to find.

Going slow buys time. An economic recovery could save some banks that would otherwise go under. But if the recovery is slow and smaller banks’ finances get even worse, it could wind up costing even more.

The bank failures, 106 in all, are the most in any year since 181 collapsed in 1992, at the end of the savings-and-loan crisis. On Friday, regulators took over three small Florida banks — Partners Bank and Hillcrest Bank Florida, both of Naples, and Flagship National Bank in Bradenton — along with American United Bank of Lawrenceville, Ga., Bank of Elmwood in Racine, Wis., Riverview Community Bank in Otsego, Minn., and First Dupage Bank in Westmont, Ill.

When a bank fails, the Federal Deposit Insurance Corp. swoops in, usually on a Friday afternoon. It tries to sell off the bank’s assets to buyers and cover its liabilities, primarily customer deposits. It taps the insurance fund to cover the rest.

Bank failures have cost the FDIC’s fund that insures deposits an estimated $25 billion this year and are expected to cost $100 billion through 2013. To replenish the fund, the agency wants banks to pay in advance $45 billion in premiums that would have been due over the next three years.

The FDIC won’t say how deep a hole its deposit insurance fund is in. It can tap a credit line from the Treasury of up to a half-trillion dollars to cover the gap.

The list of banks in trouble is getting longer. At the end of June, the FDIC had flagged 416 as being at risk of failure, up from 305 at the end of March and 252 at the beginning of the year.

Yet the pace of actual bank failures appears to be slowing. The FDIC seized 24 banks in July, 11 in September and 11 in October.

If any bank poses an immediate danger to customers or the broader financial system, regulators close it immediately, bank supervisors said. The issue is murkier for troubled banks that might qualify to close but whose closings might still be postponed or even prevented.

The FDIC’s first priority, spokesman Andrew Gray said, is to maintain public confidence in the banking system. “As evidenced by the stability of insured deposits throughout last year, this mission has been a success,” he said.

He said public confidence isn’t reason enough to delay a bank closing, because legally the decision to close rests with whoever chartered the bank — a state or federal agency.

But more than a dozen experts say the FDIC’s mission to maintain public confidence in the banking system contributes to the go-slow approach.

“The FDIC was set up to create confidence and prevent bank runs,” says Mark Williams, a former bank examiner for the Federal Reserve. Being too aggressive about bank closings “can be counter to the mission.”