U.S. bank failures will cost the government's deposit insurance fund about $14 billion next year, leaving the fund with only about $4 billion to back more than $2 trillion worth of insured deposits, Federal Deposit Insurance Corp. Chairman L. William Seidman predicted yesterday.

A reserve of $4 billion is "clearly not sufficient," Seidman said on the NBC television program, "Meet the Press." He said new sources of money will be needed to protect depositors in the nation's commercial and savings banks.

"The bankers are going to pay" for the additional money rather than the taxpayers, he said. "We think they have plenty of resources to do that. And we expect that they will agree that that's what ought to be done."

Seidman, however, has said previously that there is a limit to how much the banks can be asked to kick in without hurting both financial institutions and the insurance fund. A prolonged recession could put the banks in such a position and require taxpayer money to rescue the insurance fund, he has said.

Seidman's projections are the first for next year and reflect the continuing deterioration of the nation's economy. As the economy and the condition of banks have slipped this year, so has the condition of the bank insurance fund. Seidman's projections yesterday showed that process continuing and getting somewhat worse next year.

Yesterday, Treasury Secretary Nicholas T. Brady, speaking on the ABC television program, "This Week with David Brinkley," said there is "a significant economic slowdown" this quarter that is likely to continue into the first quarter of 1991. {Details on Page A6}.

"We expect that during 1991 it will turn around and we'll be back on the growth path," Brady said.

Brady refused to characterize the slump as a recession, but his suggestion that the slowdown will continue into next year goes beyond previous forecasts by top government officials.

While Seidman gave no specific figures on how much money will be needed to shore up the bank insurance fund, his comments suggested that he wants more than $20 billion added to the fund over the next three years on top of its annual income of about $9 billion, mostly from deposit insurance premiums paid by banks.

The FDIC fund guarantees deposits of up to $100,000 in each account in member banks and is the subject of a wide-ranging review by the Treasury.

Many financial analysts believe that the economy's downturn could provoke a rash of bank failures that, in turn, would make economic matters much worse. Former Treasury secretary William E. Simon, also interviewed on the Brinkley show, warned: "I think that a serious financial collapse of a major bank or two major banks would certainly have an effect on the economy and prolong this slump ... We have to avoid that, and we have to avoid that assiduously ..."

With the economic outlook uncertain and the cost of bank failures rising, Seidman, in an interview in his office last week, said his agency and the other two federal banking regulators -- the Office of the Comptroller of the Currency and the Federal Reserve -- are looking at how failures have been handled in recent years to see if costs can be reduced in the future.

In some cases, usually involving very small banks, the FDIC has closed institutions and paid off insured depositors. More commonly, the insurance agency has kept the bank open and sold some or all of the financial institution to a new buyer. In these cases, the insurance fund has had to add large amounts of cash to the transaction to clinch the deal.

A new approach under consideration, but not used since the Great Depression, would be to try to stave off the failure of a weakened bank by using money from the bank insurance fund to buy preferred stock in the fund while it is still solvent, Seidman said.

This infusion of cash, which would come from the insurance fund, could "get them through the worst and then the banks could buy back the stock when good times return," Seidman said.

Increasing the capital of banks could also make the institutions more willing to make new loans and alleviate a credit squeeze that has hit some parts of the nation.

Any proposal to invest federal money in banks while leaving management unchanged and stockholders still the owners could run into strong opposition, both from liberals who would see it as a bailout of wealthy bankers and from conservatives who believe the government has no business being part-owner of a bank.

"We have a group reviewing all the ways we have dealt with all these things in the past," Seidman said. "We are also looking at the political and ideological implications of these approaches."

Because of losses, particularly on real estate loans, about 175 to 180 banks, most of them small, will fail this year, according to FDIC estimates. Yesterday, Seidman gave no estimate of how many may fail next year.

A report prepared by three economists for a House banking subcommittee on the status of the insurance fund, which is scheduled to be released today, said a severe recession could boost the insurance fund losses to $63 billion over the next three years.

Seidman refused to speculate about losses to the fund beyond next year, but he hinted that if the losses were bad enough, taxpayer money in the form of loans from the Treasury to the insurance fund might be needed.

"We may be in an economic boom by that time," the FDIC chairman said, "so I don't take too seriously the three-year forecast ..."

"... at worst there would be a small additional amount needed to be borrowed from the Treasury," he said.

Earlier, Seidman had predicted that the fund would drop by about $3 billion this year. Last week, when he reported that 11.6 percent of the nation's 12,400 commercial banks lost money in the third quarter, he revised his estimate of this year's loss to $4 billion. If the estimate proves true, the fund's reserves would be reduced to about $9 billion on Jan. 1.

Slightly more than 1,000 of the nation's commercial banks remain on the FDIC's problem list. Most of those on the list are in Texas and other southwestern states, New England and other northeastern states and in the mid-Atlantic region. In all these regions, banks have suffered large losses in the wake of collapsed real estate booms.

The FDIC's bank insurance fund also covers deposits at nearly 500 thrift institutions known as savings banks. The institutions, located mostly in the Northeast, collectively lost $771 million in the third quarter and $1.2 billion so far this year. Thirty-one of the institutions are on a separate FDIC problem list, with seven failing this year.