Federal banking regulators yesterday took over the three banks owned by Bank of New England Corp. of Boston and promised to protect all depositors in a move to shore up public confidence in the region's hard-hit banking system.

The Federal Deposit Insurance Corp. pumped $750 million into the banks and estimated the rescue will ultimately cost $2.3 billion, making it one of the nation's three biggest bank failures ever.

The three banks -- Bank of New England, Connecticut Bank and Trust Co. of Hartford and Maine National Bank of Portland -- are scheduled to reopen today under the control of the FDIC, which will run the banks until they are sold or liquidated.

"We have two active bidders and other qualified bidders might apply," FDIC Chairman L. William Seidman said last night at a press conference here to announce the takeover. The identity of the bidders could be made public in a few days.

Hit hard by bad real estate loans, Bank of New England Corp. had been on the brink of failure for more than a year and was finally pushed over the edge by the region's slowing economy and the deterioration of its own business dealings.

The action taken by regulators followed a massive run late last week by depositors, who pulled more than $1 billion out of their accounts at the three banks. The Bank of New England Corp.'s disclosure Friday of huge new losses and the closing of 45 Rhode Island banks and credit unions last week, combined to batter depositors' confidence in the three banks, regulators said.

The decision by Rhode Island Gov. Bruce G. Sundlun to close the banks and credit unions, caused by the failure of a private deposit insurance system, left hundreds of thousands of New Englanders unable to get access to their money. Sundlun yesterday outlined an interim plan that would allow most depositors to receive half their savings accounts up to $2,500 and $10,000 from their checking accounts beginning Jan. 21.

Regulators had little choice but to move quickly on Bank of New England and protect all depositors, including those with accounts that exceed the $100,000 limit on federal deposit insurance, Seidman said.

"Any abrupt action at this time, in this area, was judged to be unwise," Seidman said. The FDIC chairman said Bank of New England executives met with regulators in Washington on Thursday and "essentially threw in the towel."

It was "clear that this time, to protect the stability of the system, we should protect all depositors," Seidman said

Bank of New England Chairman Lawrence Fish told regulators the losses in the last three months of 1990 were much greater than had been expected and the outlook for the future was so bleak that the bank had no hope of surviving without federal assistance, Seidman said.

After the Thursday meeting, the Office of the Comptroller of the Currency, which regulates national banks, began the process of taking over the three financial institutions. Comptroller Robert Clark and Seidman met Saturday and yesterday with officials of the Treasury Department and the Federal Reserve to work out a plan for the rescue.

The failure was no surprise to regulators, Seidman said. As a precaution, the projected cost was included in the $4 billion budgeted by the FDIC for bank failures in 1990. Thus, the rescue will not further deplete the FDIC's deposit insurance fund, which by the end of this year is expected to have just $4 billion to protect $2 trillion in deposits.

Seidman has said the FDIC needs an infusion of $25 billion to replenish the fund. There is growing concern that taxpayers will have to be asked to help out the FDIC, which is financed exclusively by fees paid by banks on their deposits.

Much of the money withdrawn last week from the New England banks came from accounts fully insured by the FDIC, a sign that depositors had been spooked by the Rhode Island credit union crisis as well as Bank of New England's losses, regulators said.

"People do not always make the distinction between private insurance and the FDIC," said Clark, who also is a director of the FDIC. "When you have people whose life savings is attached, it makes people very nervous."

"The problems came when people in blue-collar neighborhoods just got scared," said Wilbur Ross, an adviser to the New England bank's senior bondholders.

"The real problem was what would go out of the bank on Monday and Tuesday, when you would have a real panic situation," said Ross, a director of the New York investment firm Rothschild Inc.

Seidman said the cost of the Bank of New England failure will not be known for many months, but initial estimates put it in the same range as the failure of Continental Illinois Corp. of Chicago in 1984, First RepublicBank Corp. of Dallas in 1988 and MCorp of Dallas last year. The FDIC has estimated the cost of rescuing First RepublicBank at $3 billion while MCorp and Continental were projected to cost $1.5 billion to $2 billion.

Though final costs are not known, those earlier failures are turning out to be less expensive than originally projected because the government has been able to get more money back by selling assets of the failed banks.

As it did with First Republic and MCorp., the FDIC created "bridge banks" to assume control of the three New England institutions. The tactic was authorized by Congress in 1987 partly as a way to bolster depositors' confidence in the face of a major bank failure. By keeping the banks in business with federal backing, the risk of a run on deposits is reduced.

The FDIC can operate bridge banks for up to three years while it seeks new owners, but it took the agency only a short time to sell First Republic to NCNB Corp. of Charlotte, N.C., and to sell most of the operations of MCorp to BankOne Corp of Columbus, Ohio.

After the banks are sold, the FDIC will take responsibility for all their bad loans and repossessed real estate, which Seidman estimated could total as much as $5 billion.

Though the banks' depositors were protected by the government action, its shareholders were wiped out along with investors who held more than $500 million in now-worthless bonds issued by the holding company.

Bank of New England Corp., once one of the 10 largest banking companies in the nation, had been shrinking its operations under pressure from federal regulators for more than a year. From $32 billion in assets in 1989, it was down to $23 billion by last week. Its operations in Rhode Island were sold in December and the Maine bank had been up for sale for some time.

Seidman and Clarke blamed the Bank of New England failure on the crash of the Northeast real estate market. The bank was the biggest real estate lender in the region, which has suffered the worst real estate decline since Texas was hammered by the collapse of oil prices in the early 1980s.

Bank of New England Chairman Fish, who was brought in about a year ago, "has been doing everything that needs to be done" and will continue to run the bridge bank under FDIC direction, Seidman said.

The deterioration of the New England real estate market "just simply overwhelmed us," Fish said last night in Boston. "No institution in New England was as concentrated in real estate as Bank of New England."

"This is a classic lesson in failure to diversify risk," he said. "So I don't necessarily draw conclusions about other banks in the region."

One bank of New England officer has been indicted for fraud in real estate loans, but Seidman said the main problem was the bank's lending too much of money for real estate ventures.

The decision to protect all Bank of New England depositors, including $2 billion in accounts that exceeded the $100,000 limit on FDIC insurance, reflects the government's dilemma in dealing with the failure of big banks. Such banks are often called "too big to fail" because their collapse might trigger financial problems that would damage the nation's overall economy.

Special correspondent Christopher J. Daley in Boston contributed to this report.