IN THE savings and loan bill now nearing enactment, Maryland's General Assembly is making a serious mistake -- and one that it has made before. It wants to keep giving state charters to S&L associations. It is going to try once again to regulate them -- despite the massive evidence that the state is not good at financial regulation, and cannot adequately protect the public.

Both houses have now passed S&L legislation. Both would tighten the existing rules -- but both would keep the state in the business of chartering S&Ls, despite the massive scandals in the early 1960s and again last year. Sen. Stewart Bainum (D-Montgomery) led an attempt last week to end the state charters and turn over the responsibility for regulation entirely to the federal government. He was voted down, but he was right.

He lost because other senators are being pressed hard to preserve Baltimore's small ethnic S&Ls. Some are, in effect, neighborhood clubs. Some evoke powerful sentimental recollections of the years when the downtown banks wouldn't give mortgages to the newcomers from Eastern and Southern Europe, who responded by forming their own associations. But the political connections that were reflected in the Senate last week also make it hard for state regulators to enforce the rules on them.

Under the law enacted last year, all Maryland S&Ls will be required to join the federal deposit insurance system -- the big associations sooner, the smaller ones later, but all of them by 1989. That certainly constitutes a great improvement in protection to customers. But if these S&Ls are going to have to join the federal insurance system, what's the point in continuing to have the state charter them? Why get into double regulation by both the federal and state authorities?

The answer is not reassuring. Some of the small S&Ls are going to have trouble meeting the requirements for federal insurance. You can already hear the whispered suggestions that perhaps there ought to be an exemption for them, allowing them to continue under state insurance.

The Senate, in the bill that it passed last week, included an ominous provision allowing these small thrifts to seek waivers from any of the new state rules that would cause them "undue hardship." Does it mean that, in a year or two, there will be a further bill to exempt them from the hardship of qualifying for federal deposit insurance?

If the General Assembly intends to stand by its insistence on federal deposit insurance, there is no reason to continue the state charters after 1989. For all the reasons that the past year's events have graphically demonstrated, the only defensible choice for the state of Maryland is to get out of the regulation of S&Ls -- to get out promptly, completely and permanently.