AGATHA -- AMC Carrollton, Beacon Mall, Fair City Mall, Roth's Manor, Roth's Randolph, Tenley Circle.

The question in "Agatha" is not whodunit, but who dun what ?

When Agatha Christie died in 1976, she had produced an extraordinary number of amazing mysteries. Her life, as an honored writer and the wife of a British archeologist, was not one of them, although she preferred to conduct it out of the glare of celebritydom.

But 50 years previously, during an unsuccessful first marriage, Agatha Christie had inadvertently caused a public stir by slipping away anonymously for 11 days.The sad but hardly mysterious desire to be by herself during a period of unhappiness has been given the ace mystery treatment by writer Kathleen Tynan, first in a book and now in this film. Christie, being dead, is beyond even England's libel laws, leaving Tynan free to suggest that she spent those 11 days plotting a peculiarly undignified crime and, what's worse for her professional reputation, executing it clumsily and unsuccessfully.

Everything that can be done by tingly music, scenes half-hidden in billowing smoke and fearful stares has been put into this film to make it seem sinister and scary. Deluxe restaurants and hotels are photographed in such a suggestive haze as to make one wonder why the management doesn't air them before the customers complain.

Vanessa Redgrave's blue eyes look out in bewildered terror on everythign. One may believe that anyone is capable of going temporarily demented from romantic rejection, but this Agatha Christie is shown throughout as being pathetically weak, not only emotionally but intellectually. When she attempts to destroy the childishly clear notes she has made in preparation for her crime, she fails to notice that she has left them behind still in a readable state. It's a harsh portrait of nervous feminine incompetence that makes one sympathize with the husband's desire to throw her off. Redgrave is somewhat big to act clingy.

But a stranger character yet has been put into Agatha Christie's life. Dustin Hoffman plays an American newspaper columnist of apparently unprecedented wealth and prestige, who follows Christie to her retreat and pesters her with nasty attentions that we are expected to believe are the birth of love. As he is incredibly ostentatious and vulgar, with trunks full of silk shirts and an unquenchable desire to impress tradesmen, there's an implication of evil that adds to the unjustified menace of the film, if it doesn't set one laughing instead. But his rattiness is supposed to come off as generosity.

Other small, careless mysteries abound in this film. dChristie's hideaway is a large spa. She arrives without luggage, which is not questioned by the hotel, and is apparently able, without revealing any identity, to run about town buying furs and clothes. Nor does she sttempt to disguise herself, and although her photograph is on the front of every paper in the place, no one makes the connection for days, not even her husband's secretary-mistress who might be supposed to be preoccupied with the disappearance.

Altogether it is, one could say, a nasty piece of work, if not a crime.