THE NEXT STAGE of Maryland's struggle with the failed savings and loan associations will be an investigation into possible fraud and theft. But the troubles of the S&Ls, in Maryland and throughout the country, go far beyond the few spectacular cases in which there is evidence of financial crime. The fundamental reason for their distress is that the traditional S&L, whose principal business is mortgage lending, is not well adapted to survive amid high and unpredictable interest rates. The isolated cases of illegality are having extraordinary reverberations because of the strain on the whole financial industry. The public responsibility here is, above all else, to protect and guarantee the depositors' money.

The most spectacular collapses of the past several months have taken place among privately insured S&Ls in two of the six states that permitted private deposit insurance. But even among the federally insured S&Ls there has been a dramatic death rate in recent years. At the end of 1980 there were 4,002 federally insured S&Ls; currently there are about 3,100. Of the 900 that have disappeared, most failed or were quietly merged out of existence because they were in serious trouble. That kind of trouble is not limited to S&Ls alone. Nationwide, since the beginning of this year, some 35 banks have failed.

In Maryland, the immediate question is protecting the depositors -- first, the depositors in the S&Ls that have now collapsed, and beyond that the depositors in those institutions that will be forced out of business because they are not able to meet the standards for federal insurance. Gov. Harry Hughes, to his great credit and the state's, has accepted a broad responsibility for funds that most depositors thought, mistakenly but understandably, were insured by the state. Are the taxpayers going to have to make good all of those losses? It would be far better to let banks from other states come into Maryland and buy those troubled S&Ls where they are willing to do it.

Gov. Hughes and the Maryland legislature can be chided for waiting too long. But when the dimensions of the emergency became clear, they moved rapidly and effectively.

Meanwhile the White House refuses even to acknowledge that anything needs to be done for or about the financial system -- except, of course, further deregulation. Most of Congress is uneasily aware of a need for legislation, but neither of the banking committees is making much progress toward the broad reconsideration of the financial rules that is now essential. Institutions that take deposits from the public have special obligations. In their scramble for growth, some of them seem to have lost sight of those obligations. The events in Maryland, like those earlier in Ohio, are a warning.