Dame Agatha Christie, that English gentlewoman who plotted devilishly fiendish ways of killing people as she munched on apples, wrote "Murder Is Easy" in 1939 during her vintage years.

Tonight CBS is offering an updated adaptation of the Christie mystery with an amateur sleuth who uses a computer to try to help trap the murderer. None of those "little grey cells" of Hercule Poirot or Miss Marple's observations on human nature as the knitting needles click.

But Christie fans need not be indignant. The two-hour TV movie, to be shown at 9 p.m. on Channel 9, is not disrespectful of Dame Agatha. It keeps her sleight-of-hand plot tricks while shifting characters and story to the contemporary scene. "Murder Is Easy" turns out to be a sprightly film with an ingenious puzzle, a nice touch of romance, and a clutch of those eccentric character types who seem to inhabit all small English villages.

Olivia de Havilland and Helen Hayes, appearing as special guest stars, obviously have great fun in their roles. And that fine actor, Timothy West, is a marvelous hot-tempered, self-made British lord of the manor. Bill Bixby, with a nice American face for an MIT computer researcher, and Lesley-Anne Down, who can be as sultry and seductive as Ava Gardner, are the likable young people who find romance in the midst of six murders.

"Murder is Easy" (which appeared in the United States under the title "Easy to Kill") is one of Dame Agatha's small triumphs. A non-Poirot, non-Miss-Marple mystery from Christie, it offers some excellent murders spiced with a love story. It features an engaging amateur sleuth who comes up with a credible solution.

On a train bound for London, Luke Williams (Bixby), a vacationing American computer expert who programs the winner of the English Derby, meets Lavinia Fullerton (Hayes). She is on her way to Scotland Yard because she doesn't believe the police constable in her village of Wychwood is the man to deal with three murders.

And who can blame Luke for first suspecting that Lavinia is one of those dotty English ladies with stout shoes, a capacious handbag and a suspicious nature. Then Lavinia is killed by a hit-and-run driver minutes after they get off the train in London, leaving Luke to remember her words:

"When not one suspects you, murder is easy."

Luke, his curiosity piqued and his conscience a bit uneasy because of his disbelief in Lavinia's story, goes to her funeral in Wychwood. There he finds there have been other "accidents."

And there is no scarcity of suspects -- Lord Easterfield (West), who speaks of wreaking revenge on those who have crossed him; Bridget Conway (Down), Easterfield's young secretary-fiance'; the young doctor who is mysterious about the needle marks found on a dead housemaid's arm; the bearded antique dealer who praises drugs as a creative inspiration; the solicitor who is a womanizer; the hearty retired major who likes dogs better than people.

Luke learns the secrets hidden under the seemingly placid surface of the English village. Miss Waynflete (de Havilland) once had been engaged to Easterfield. Bridget's father had owned the Easterfield manor house before he lost his fortune.

Scriptwriter Carmen Culver has adapted the Christie novel with some light touches of his own. Luke uses an Oxford University computer to program suspects, method of death, motive and opportunity so as to catch the reaction of Bridget, whom he both loves and suspects of murder. In the end, there's a confrontation scene that is somewhat contrived in drawing out suspense before revealing the identity of the murderer.

David Wolper, the executive producer, filmed the Christie adaptation on location in England. It's really quite handsome and evocative of the picturesque English village, which has the highest homicide rate in mystery fiction.