TO LOOK ON the bright side of the S&L disaster, both the regulators and Congress are now demonstrating that they have learned a lot from it. Those lessons are going to be valuable as the country deals with the troubles of the commercial banks. In a desperate attempt to keep failing S&Ls in business, the people who made policy not only allowed them to operate with no capital but let the federal S&L deposit insurance fund itself go bankrupt. That's why the cleanup costs are falling directly onto the taxpayer -- and it's a mistake that isn't likely to be repeated.

For one thing, L. William Seidman, the chairman of the federal Deposit Insurance Corp., is a much tougher item than any of the regulators who presided over the S&L industry's downfall. For another, in Rep. Henry B. Gonzalez (D-Tex.), the House Banking Committee has an independent and determined chairman -- a strong contrast to his predecessor.

This week Mr. Seidman proposed raising the insurance premiums for deposit insurance by more than half. Banks now pay 12 cents a year for every $100 in deposits, and the insurance fund is in its third consecutive year of heavy losses. The insurance is clearly underpriced. Mr. Seidman would take the rate up to 19.5 cents.

Mr. Gonzalez has responded by asking whether the rate shouldn't be raised still higher, to 23 cents. Even at 19.5 cents it would take at least five years to build the fund up to the amount that Congress has set as a mandatory level of reserves. Five years seems to Mr. Gonzalez a bit too long to reach the minimum standard of safety.

Even Mr. Seidman's proposal would cost the banks more than a billion dollars a year. So far the bankers aren't fighting it, but they point out that the cost will make it harder for them to raise the additional capital for which the regulators are also pressing them. Higher insurance premiums, higher capital requirements and tighter rules on lending are all going to make it a little harder for borrowers to get loans.

The national economy is slowing down, and that's one of the reasons for it. The country rode through the 1980s on a tremendous wave of borrowed money, and now it sees the dangers into which it has allowed itself to slide. Both borrowers and lenders are getting more careful -- with, in the banks' case, forceful encouragement by the people who make the rules. It probably means that Americans won't have quite so much fun spending money in the 1990s as in the recent past. But it also means less risk of another immensely expensive financial collapse.