THE banking industry's financial problems are also proving to be a pain in the pocketbook for their customers.Even as many banks work out problems in their real estate loan portfolios, legislation passed by Congress last month will mean further costs to be passed along to depositors, borrowers, and shareholders. The bill authorizes the Federal Deposit Insurance Corporation to borrow $70 billion from the United States Treasury to cover depositors' losses in bank failures. Healthy banks would repay the money over the next 15 years in higher premiums to the FDIC's Bank Insurance Fund (BIF), which is now almost empty. Robert Litan, a banking expert with the Brookings Institution, predicts banks will "eat" half the cost of thehigher premiums - cutting annual earnings by perhaps $500 million. Banks already pay the FDIC 23 cents a year for every $100 dollars on deposit, while earning an average of 60 cents for each $100 of assets. "As the recovery gets under way [in the US economy], banks are going to keep their margins [income on loans] relatively high," Mr. Litan says. Small-scale depositors will bear much of the burden of replenishing the BIF, predicts Andrew Brimmer, a bank consultant in Washington. Depositors may earn lower rates of interest on account balances and pay higher service fees. Further, getting loans is likely to become tougher for individual consumers and small businesses, the borrowers most dependent on banks, Mr. Brimmer says. The banking bill, because it includes strict guidelines requiring federal regulators to deal more quickly with failing banks, is already having a "chilling effect" on bank lending, he says. And the $70 billion may run out by 1993 or '94, Litan adds, raising the possibility that taxpayer money may be needed the next time the fund runs dry. There is some cheerier news for the industry. Capital-to-asset ratios, a measure of bank solvency, are at the highest levels in 15 years, notes Mark Lynch, an analyst with Bear Stearns, an investment house in New York. In part, these ratios are moving up because of new international requirements that go into effect at the end of 1992. Most large banks already have capital above the 4 percent of assets that will be required. With their capital levels high, the challenge for banks is "finding a place to put it," Mr. Lynch says. The bill passed by Congress gives "no opportunity to reverse the trend of the last 30 years" in which other types of financial service companies have been taking business away from the nation's 12,000 commercial banks. The Bush administration had proposed broadening the range of businesses banks could enter. The industry's "nonbank" competitors, such as insurance companies, finance companies, and brokerage houses, face neither the tough capital standards or the federal deposit insurance premiums that banks must meet. As a result of outside competition, bank loan portfolios became both less profitable and riskier during the 1980s, says Gary Gorton, a finance professor at the University of Pennsylvania's Wharton School in Philadelphia. Still, bank industry assets have grown from $2 trillion in 1981 to $3.4 trillion last year, in part because of the lure of federal insurance for deposits. Mr. Gorton says Congress should enact broader reforms to address this structural problem of overcapacity in the industry. The recently passed bill, which President Bush is expected to sign, "just accepts that more banks are going to fail," he says. "It throws a small amount of money at the problem."