WHEN W. DALE HESS, a crony of Marvin Mandel's and convicted along arrived in jail, his fellow inmates came to counsel him. They told him that his sentence -- a B2 -- meant that he could be paroled at any time. W. Dale Hess was told that he and Marvin Mandel would soon be free men. It didn't happen. Instead, the government has thrown away the keys.

Hess can blame Mandel. Not only has the former governor been effectively denied parole, but his case has been handled like a hot potato. First it was bucked from the regional parole office in Atlanta to the national commission in Washington and then it was sent back to Atlanta. The result was that Mandel was given a one-year reduction in sentence -- announced with great fanfare but signifying, truly, next to nothing. This was mostly time that was coming to him anyway.

To understand that, you have to understand all kinds of concepts of time. There is "good time" and "extra good time" and even something called "camp time." The upshot is that when all these various kinds of time are added up, Mandel's sentence would have been cut by almost a year anyway. What the parole commission gave Mandel was a reduction in sentence of anywhere from 17 to 40 days -- depending on who's doing the figuring.

There is a strong belief in this country that white-collar criminals are coddled and that politicians, in particular, get away with murder. Certainly there is something to this. White-collar criminals do, as a rule, get more lenient treatment than other kinds of criminals, but then they usually don't kill people or maim them or rape them. As for politicians getting away with murder, there is something to that also. Richard Nixon and Spiro Agnew are living example of the truth of that.

Mandel himself attributes his lack of parole to politics. A conspirator himself, he tends to believe in conspiracies and he thinks that the Carter administration is out to get him. He and his former fellow governor, Jimmy Carter, have never liked each other and in 1976 Mandel backed California Gov. Jerry Brown in the Maryland primary. "We beat Carter and we beat him badly in Maryland," Mandel told The Atlanta Constitution. "And he [Carter] has never forgiven that."

You would have to have a pretty dark view of Jimmy Carter to believe he cared albout keeping Marvin Mandel in the clink. But that does not mean that Mandel and the claque he has chanting for his freedom, are not right on the large point that the parole board is being unduly severe. This is the view, in fact, of the U.S. attorney for Maryland, Russell Baker, who wrote the parole commission, saying the decision to have Mandel serve what amounts to the maximum sentence is "unecessarily severe."

The explanation for the parole board's insistence that Mandel serve what is known as "max" has probably more to do with publicity than anything else. The board has already shown itself to be a bit skittish in dealing with Mandel and it probably figured that the safest thing to do was to announce a reduction in sentence that was not a reduction in sentence at all.

In this way, the board had the best of all worlds. It did the humane thing and also protected itself against criticism that it was coddling a white-collar criminal --giving yet another politician a free ride. The way things stand now, though, no one could say Mandel is being coddled. In fact, he is becoming something of a martyr.

If Mandel serves the full term of 24months, he will have spent more time in jail than either John Ehrlichman or H. R. Haldeman, Nixon's White House aides suring Watergate. They both did 18 months. As for John Mitchell, the former attorney general, he, too, did what seems to be the customary 18 months. Even if you compared Mandel with his contemporaries in Maryland political corruption his sentence seems harsh. Dale Anderson the former county executive of Baltimore County, served only 13 months of a five-year term for conspiracy, extortion and tax evasion. Compared with what Mandel did -- a little sleight of hand with a race track -- Anderson was the equivalent of a mass murderer. Similarly, Joe Alton, once the county executive of Anne Arundel County, served only six months for getting kickbacks.

The question here is not whether Mandel deserves to spend two years in jail, but whether he is doing so for reasons having nothing to do with his crime -- the reluctance of the government to seem lenient toward a prominent politician. If that is the case, then Mandel is being punished for what he is as much as for what he did. He should not be given any breaks because he was once a governor. But he should not be punished for it, either.