IT IS POSSIBLE that Marvin Mandel may never fully understand why his way of life as a public servant led to yesterday's criminal conviction. After all, this was the only kind of politics he and many others ever knew - and it was a politics that seemed to bear no malice toward the people he served. And anyhow, in Annapolis, Baltimore and too many other reaches of Maryland over the years, people had customarily demonstrated the warmth of their feelings toward public officials by giving them gifts: cash, cutins on highly lucrative business deals, clothing, jewels and vacations. And Mr. Mandel acccepted all these, insensitive to any possible implications of impropriety or illegality.

That deep-seated insensitivity was apparent again yesterday when Mr. Mandel expressed his shock at the verdict. "I'm not walking out feeling that I have done anything to hurt the people of this state," he said. "I love it too much to have done anything to hurt it." How sad that a man has been convicted who involved himself so vigorously and sincerely in the service of his state and who had ambitions, many of them realized, to improve the welfare of his state. His managerial instincts were as sharp as his political acumen. But these attributes were to be negated by Marvin Mandel's inability to draw a proper line between private relationships and public business, between the public obligations of those who run the government and the personal interests of those who do business with it.

It is noteworthy, too, that the verdict was rendered by 12 citizens from mr. Mandel's beloved state, where cronyism is not exactly a strange phenomenon. After a remarkably lengthy set out deliberations, this jury concluded to a person that the governor's ways of friendship had been sufficiently spelled out to be adjudged criminally wrong. Though this legal judgment obviously did not come easily, the ethical questions were readily answerable on the basis of the trial testimony. What came through clearly in the case of the United States vs. Marvin Mandel and his friends was a seamy set of relationships that - however commonplace such things may have been in this state before - were ethically improper and a threat to the integrity of the state's executive branch. Ideally, the revelation of these details, coupled with the verdict, will have a useful effect on politics throughout Maryland, contributing - at least so we hope - to a better standard of conduct for officials at all levels of state government.

There are other questions, of course, still to be answered, not the least of which involves the appeals to be filed by Mr. Mandel and the other defendants. Another piece of unfinished business concerns the alleged jury tampering that led to a mistrial the first time around: the efforts of prosecutors to get to the bottom of this curious development should continue.

Finally, there is the most important matter of how Mr. Mandel will formally and fully relinquish the governorship. As we understand it, under the law he may stay in office until time of sentencing, scheduled for Oct. 7. But since Mr. Mandel has for health reasons already transferred many of the powers to Blair Lee III, we see no public benefit in his reassumption of authority now. Marylanders deserve to get their government out from beneath the dark cloud that has hovered over it for too long, and that can't happen with a convicted lame duck in the top job. We urge Marvin Mandel to resing - now.