WASHINGTON — Regulators expect the cost of bank failures to grow to about $100 billion over the next four years — up from an earlier estimate of $70 billion.

Faced with that sobering news, they voted today to require banks to prepay $45 billion in premiums to replenish an insurance fund that will start running dry on Wednesday.

The proposal by the board of the Federal Deposit Insurance Corp. to require early payments of premiums for 2010-2012 could take effect after a 30-day public comment period.

The FDIC is fully backed by the government, which means depositors' money is guaranteed up to $250,000 per account. But it would be the first time the agency has required prepaid insurance fees.

The insurance fund has been sapped by billions from a rash of bank failures that began in mid-2008. The banking industry prefers the prepaid premiums over a special emergency fee, which would be the second this year.