BY NOW ONE CAN predict that when reformers set out to purify some part of public affairs, they will prescribe strong remedies and then find out that those remedies are too harsh, annd fall back awkwardly to a more sensible plan. That is what has happened with the part of last year's Ethics in Government Act that sharply curbs federal officials' professional activities after they leave the government.

The legitimate point of the law was to bar ex-officials from exploiting inside information and connections or "switching sides" to represent an outside interest on matters they had dealt with while in government. But Congress and the administration were determined to proscribe every kind of exertion of influence, direct or indirect, that could conceivably be abusive or unethical. The result was a criminal statute so broad and indistinct as to deter a top-level official from going to work, within two years, for any company or institution that had any business with his former agency. No wonder there was so much talk about a mass exodus of scientists, educators and technical managers before the law took effect on July 1.

Predictably, the law's drafters now maintain that the most drastic readings of the law were not what they had in mind at all. And after much travail and considerable craftsmanship, the new Office of Government Ethics has indeed produced regulations that construe the law in much more reasonable and limited-though inevitably complicated-ways. The "regs" released last week declare, for instance, that a former top official may indeed take a management job at a research lab that gets grants from his old agency-and may lawfully talk with his new colleagues at lunch about the programs he used to run. Three amendments being advanced by the administration and key congressmen would resolve additional problems that even the most ingenious regulations cannot solve.

If the regulations and amendments are adopted, as they should be, the administration and Congress will wind up in a much better place-indeed, one better in some respects than they deserve. But the whole experience should be one more caution to those, in and outside of government, who persist in trying to solve every ethical problem by law. Human relations-and relations between government and the rest of society these days-are not at neat and codifiable. Next time around, we hope the champions of public virtue will think twice before they pass a comparable "reform."