IN SENTENCING MARYLAND Gov. Marvin Mandel to four years in prison on mail fraud and racketeering convictions, U.S. District Court Judge Robert L. Taylor quite understandably observed that the case "has given me as much or more concern than any case I have ever tried." Reflecting what must be the sentiments of so many people in the state, the judge told Mr. Mandel: "I have great sympathy for you. You have many, many good qualities. I think you made some serious mistakes."

That said, Judge Taylor's sentence seems neither excessively harsh nor overly soft when compared with other more or less similar cases. Mr. Mandel, who will be subject to parole at any time if the sentence is actually served, is after all paying a considerable price as a disgraced governor. Interestingly, the judge said he did not fine the governor because he believes Mr. Mandel to be insolvent. Similarly, the judge sentenced one of the governor's codefendants to 18 months without fine. Three other more well-to-do principals in the case - W. Dale Hess, Harry W. Rodgers III and Irvin Kovens - received four-year prison terms and $40,000 fines. Mr. Mandel and all codefendants remain free pending appeals.

Meanwhile, Mr. Mandel's refusal to resign leaves Maryland with a convicted, suspended governor, an acting governor and no lieutenant governor - a state of affairs that could last for a year or more while the case is on appeal. According to an interpretation from his attorney general, Francis B. Burch, Mr. Mandel only had to transfer all powers of the governor - not the official office - to Acting Gov. Blair Lee III.

While we sympathize with Mr. Mandel's sense of personal pride and his financial hopes for full retroactive benefits if his conviction is overturned, the situation is awkward. An acting governor cannot act with complete authority so long as there is any question about his tenure. Moreover, any reassumption of the governorship by Mr. Mandel between now and January 1979 - when his term would have ended, anyway - would surely be disruptive. So for the time being, Acting Gov. Lee is left with the difficult and delicate task of trying to restore respect for an office he hasn't fully inherited.