Three primes were enough for Miss Jean Brodie. The imperious and ethereal teacher created by Muriel Spark has already been portrayed in book, play and movie. Now a Scottish television production comes to American public TV, and it can only be recommended for those who've not had the mixed pleasure of meeting the character before.

Otherwise, those smitten with Zoe Caldwell's barnstorming stage portrayal or Maggie Smith's fling as the schoolmarm in the 1968 movie version-both performances as formidable as runaway trains-will find little added to the TV version but length. "The Prime of Miss Jean Brodie," starting tonight at 9 on Channel 26, will take five more hours, on succeeding Monday nights, to unfold.

This time the dictatorial romantic with a naive yen for Italian fascism is played by Geraldine McEwan, who is certainly thoroughgoing in the part-it's a fanatical depiction of a fanatic-but who fails to bring all of Miss Brodie's camouflaged and sinister charm to the surface.

Miss Brodie arrives at a strict private school for young women in 1930 and, as Caldwell and Smith played her, manages to lure both her girls-or "gells," as she broguishly calls them-and the audience into her flamboyant hallucinations-until their darker side is revealed. But as McEwan plays her, she is on the demonic side from the outset, even when airily declaring, "Where there is no vision, people perish," or telling her enthralled class, "One's prime is the moment one is born for, and you shall have the fruits of mine."

What the TV production-the work of four writers and three directors-does have over previous "Primes" is authenticity of location and a detailed evocation of academic isolation-of a formal education as it used to be. The first chapter includes, on tape, handsome, brooding views of Edinburgh, a city in which, at least for the purposes of this show, all that is not brown is gray.

Anyone not familiar with the story of Miss Brodie from other incarnations may be pleased to make her acquaintance on TV, even if exhaustion sets in rather quickly. What everyone has a right to resent is the way WQED, the importing PBS station in Pittsburgh, has tacked on those standard celebrity introductions and afterwords to tell us what we will see and have seen and what to think of it.

"We first meet Jean Brodie . . . .," Julie Harris says before the play; ". . . . and so we have met Miss Jean Brodie," she says when it's over, as if we were little "gells" ourselves and listening to a fairy tale on the radio. Writer Harvey Jacobs gave Harris such a mouthful of unnecessary footnotes that she very nearly explains the play to death. This kind of packaging is as irritating as it is trite, and entirely too de rigueur.