Agnew case revisited; Go Quietly or Else, by Spiro T. Agnew. New york. William Morrow & Co. $10.95.

Here's a book for anyone who wants to reopen the pages of the Agnew affair of seven years ago. But few probably will. At first reading it seems straightforward enough -- the former vice-president wants us to believe he's really an innocent man wronged by our judical system. But it quickly gets more complicated. for one thing, in the final analysis he is precisely the one who could have prevented the "wronging" but didn't -- because he didn't contest a criminal charge of evading income taxes. And he also permitted, as the result of plea bargaining, a 40-page list of evidence against him in this and other cases to be made public.

As a result he had to resign the vice-presidency in disgrace. And, because his nolo contendere plea resulted in his becoming a convicted felon, he was predictably prevented from practicing his vocation thereafter -- he's lawyer.

Would a person as innocent of wrongdoing as he claims have acquiesced in all this? doubtful. That the question should be asked at all stems from the nature of a nolo contendere plea -- it prevents evidence in a case from being presented in court. And, therefore, from having the full evidence on both sides made public.

Not surprisingly, the evidence Mr. Agnew offers here would weaken the case against him. He holds that overzealous prosecutors -- whom he calls "The Gang of Four" -- combined with business associates and friends to charge him with crimes he did not commit. And that there was no independent corroboration of evidence against him.

We cannot know precisely what prosecutors would say to that now, which is why the careful reader would delve more deeply into the Agnew book of clues withing. And it is here that the former vice-president frequently weakens his case.

To begin with, he admits his own lawyer apparently believed the charges against him were provable. if he were in fact innocent, why not change lawyers?

The heart of the allegations was that he had accepted contributions from engineering firms in return for providing them with government contracts -- in other words, that he took brides. He vigorously denies this.

But he says that, as maryland's governor, he did accept contribution from businessmen and, "Of course, I would give the jobs to my friends whenever they were fully qualified to do the work; why on earth should I give them to my enemies?" Such selection by the governor, he insists, had been "a normal thing" in Maryland -- a chilling thought.

Agnew's rational arguments are marred by the bitterness he feels -- toward the Justice Department for its leaking of evidence to the press, toward the Nixon White House for having shunned him, toward presecutors and former associates.

They're marred, too, by his instance that so many factions were out to get him -- prosecutors, attorney general, press, liberals, and White House officials. He even believes that Alexander M. Haig Jr., a Nixon White House chief of staff, issued a velied threat to have him killed if he did not resign.

Altogether, it's little too hard to believe.