A little-known group of hybrid financial institutions that are part bank and part savings and loan have emerged as a new problem for federal banking regulators.

The nation's 465 savings banks are suffering from the same bad real estate loans that have infected the banking and savings and loan industries and upwards of two dozen of them -- some worth more than $1 billion -- are now expected to fail, government officials and private banking experts agree.

Prevalent in New England, savings banks are state-chartered institutions that nevertheless are insured by the Federal Deposit Insurance Corp.

The savings banks won exemption from the restrictions on high-risk investments such as junk bonds and real estate speculation imposed in last year's savings and loan cleanup bill by arguing that they were not suffering from the same problems that wiped out the savings and loan insurance fund.

But since then, the economy of the Northeast has slipped into a recession, and the savings banks are looking more and more like the S&Ls of the Southwest, posing a threat to the FDIC fund that protects depositors when banks fail.

Provisions for potential savings bank failures are one of the reasons FDIC Chairman L. William Seidman recently added $1 billion to his estimate of how much the fund will lose this year, raising the projected loss to $3 billion. To pay for the losses, the FDIC recently raised the insurance premium it charges banks, including savings banks.

Because of the savings banks' unusual niche in the nation's banking system, the FDIC has never included them in its regular reports on the health of the banking system, but now FDIC statisticians are preparing a special report to the FDIC's board of directors on the problems of the savings banks.

"The industry as a whole is sound, but we have some problems," said an FDIC official who asked not to be identified. "There are some that are suffering from {past-due} loans. There are some that are not going to make it."

Private analysts state the problem even more bluntly.

"There are a number of relatively large New England thrifts that will definitely not make it," said Don J. Kauth, a banking specialist with First Albany Corp., an upstate New York investment firm.

"You'll see a number of failures and government-assisted transactions" to sell savings banks, agreed Bruce Harding of Salomon Brothers Inc., the New York investment banking firm.

Data gathered from private sources and interviews with government officials and industry analysts make clear that the savings banks are in trouble. They show:

The savings bank industry as a whole is losing money. The biggest savings bank in the nation is already broke and all-but-certain to require a government rescue costing upwards of $1 billion. Six New England savings banks with more than $1 billion apiece in deposits are struggling to survive.

The General Accounting Office said three savings banks are among the 20 substantial bank failures that are expected to occur in the next few months, although that detail was not mentioned when the GAO predicted the failures last month.

Federal regulators project that as many as three dozen savings banks may fail, and private experts are no more optimistic.

Half a dozen savings banks have failed since the real estate markets in the Northeast started to slide, and more are headed in that direction, predicted James Moynihan, a Boston banking specialist with Advest Inc., a regional brokerage firm. "The entire New England scene has been deteriorating ... since January of '87 and it isn't getting any better."

Moynihan predicted substantial FDIC losses in Massachusetts, which has the most serious real estate troubles, the most savings banks and the most failures so far.

Connecticut "has deeper problems than Massachusetts," he added. "Connecticut has always lagged Massachusetts," and its problems are just now showing up as real estate ailments spread down from Massachusetts and up from New York.

In New Hampshire and Maine -- where the savings bank troubles are fast approaching a crisis -- six of the seven largest institutions are struggling to survive, Kauth said. Each of them has more than $1 billion in assets, and if all six were to fail, the total cost to the FDIC could easily exceed $1 billion.

The largest savings banks and the largest potential losses to the FDIC are in New York state. Harding said several institutions began suffering when the Manhattan condominium market fell apart in response to the declining fortunes of Wall Street firms and the big banks.

As a group, the savings banks lost $426 million last year, plus another $52 million in the first three months of this year, according to the latest industry reports from W.C. Ferguson & Co., a Washington and Dallas firm that specializes in banking data.

Ferguson's statistics show the savings banks wrote off $1.3 billion in loans as uncollectable in the 12 months ended in March. Their bad loans jumped from $4 billion to $6.5 billion during that period and are still growing unchecked.

Fortunately, the savings banks were in unusually strong financial condition when their problems began to develop, because many of them took advantage of the boom markets of the mid-'80's to sell stock and build up their capital.

"The New England thrifts had more capital to lose than the southeastern and southwestern ones," Kauth said. "The question is whether the nonperforming assets will outlast the capital."

Ironically, it was the sales of stock to build up their capital that got many savings banks into trouble. After they raised the additional capital, the banks had to put it to work, so they invested heavily in real estate.

The result was exactly what happened in Texas a few years earlier: The thrifts took advantage of laws allowing them to switch from their traditional home mortgage business into commercial real estate, made huge bets and lost.

Their strong capital has enabled most of the New England thrifts to absorb their losses so far, but analysts said the worst is yet to come.

One sign of trouble ahead is that prices of the stocks of savings bank companies are continuing to decline. "I don't see any sign of the savings bank stocks turning around. If the market is the proper tool {for making predictions}, we have a way to go," Moynihan said.

Kauth said he believes "a dozen Massachusetts thrifts are immediate candidates to be taken over" and that there are big failures coming soon in Maine and New Hampshire. "New Hampshire Savings currently appears to be the most vulnerable to failure," he said, and OneBancorp., the biggest savings bank in Maine, is "unlikely to survive as an independent entity."

The biggest question mark in the savings bank business is the biggest savings bank: Goldome of Buffalo, N.Y., with $10 billion in assets. It has been insolvent for several years but is being allowed by the FDIC to continue operating.

Goldome had debts that exceeded its cash assets by $467 million as of April 1. To meet future capital standards, Goldome will have to raise an additional $300 million in capital. Coming up with nearly $800 million will be virtually impossible, the investment analysts said.

Goldome's finances are so bad that regulators could shut it down at any time. FDIC officials would not comment on why they have not moved in.