A beautiful production and several adept performers, notably Dustin Hoffman in one of the most winning portrayals of his career, make "Agatha" a surprisingly glamorous, intoxicating entertainment.

The young British director Michael Apted establishes himself as a promising romantic stylist with this best-of-all-possible-improvements on the source material, Kathleen Tynan's idle fictional speculation about the brief disappearance of mystery writer Agatha Christie back in 1926.

Apted endows the film with a rapturous visual elegance. The sense of composition, atmosphere, decor and detail guiding the movie imposes a texture vastly richer than the prose style of the book, which seemed fastidiously underwritten. The movie invites you to luxuriate in its appearance and you're glad to oblige.

The muted colors and chiaroscuro lighting schemes produce some breathtaking effects. Cinematographer Vittorio Storaro achieves a wonderful illusion of soft, diffused sunlight in the interiors of hotels, restaurants, homes and offices. In one night scene he throws a reflection of a rain-spattered window on a bedroom wall that tempts one to break into applause.

The most spectacular effect occurs when Vanessa Redgrave as Agatha is seated alone in a train compartment, her face entirely shadowed, her cloche hat softly illuminated. Suddenly the lights of a passing train hurl jagged flashes of light on Redgrave's striken face. What Storaro and his crew don't know about the creative possibilities of light sources may not be worth knowing.

Pictorial knockout that it is, "Agatha" remains dramatically compromised by Tynan's trumped-up mystery plot, at once flimsy and presumptuous. It's not difficult to see why the Christie heirs took offense at the book. There is something offensive about turning a merely unhappy or embarrassing episode in a famous person's life into a coyly gruesome fabrication.

Distressed by the death of her mother and the dissolution of her first marriage, Agatha Christie vanished for 11 days in December of 1926. She reappeared at a hotel in Harrogate, a health resort in Yorkshire, where she had registered under the surname of her husband's mistress, Nancy Neele. The family ascribed the escapade to amnesia. Two years later the Christie were divorced. Col. Archibald Christie went on to marry Nancy Neele. In 1930 Agatha Christie remarried and spent the rest of her long, phenomenally productive life with her second husband, the archelogist Max Mallowen.

Since Agatha had notified her brother-in-law of her whereabouts a few days after arriving at Harrogate, the family presumably knew where she was and preferred to respect her need for a getaway until the press and police became too insistent. Tynan's notion is that Agatha is a rejected wife teetering on the edge of madness, a shaky supposition magnified in its dubiousness by Redgrave's statuesque presence. Looking majestically beautiful yet inconsolably crazy-eyed and distressed, Redgrave tends to overwhelm the role with suffering.

Tynan, who shares screenplay credit with Arthur Hopcraft, lacks the adroitness at the fact-fiction charade that one finds in Nicholas Meyer's "The Seven Percent Solution" or "The West End Horror." It seems mean to imagine Agatha Christie actually contemplating foul play as a result of her marital rift. Tynan probably doesn't intend to be insulting, any more than the copywriters intend to be insulting when they claim, inaccurately, that the plot of "Agatha" is "far more suspenseful" than anything Christie ever wrote. Nevertheless, the effect is ugly.

Tynan's contrived explanation for Agatha's flip-out also creates grievous storytelling problems. There's no place to go with the fiction that some thing drastic might have almost happened to Agatha. Since nothing bad became of the real Agatha Christie, whose identity is being toyed with on this occasion, the pretense that she's a heroin in potentially fatal distress won't quite play.It's as self-defeating as that great anticlimactic movie title: "The Woman They Almost Lynched."

The movie comes close to finessing the problem on the strength of Hoffman's undersized but potent charm. Cast as a fictional character named Wally Stanton, an ambitious journalist who traces Agatha to Harrogate and then gallantly comes to her rescue after falling in love with her, Hoffman introduces an unconventional romantic note that promises to redeem the plot. Ultimately, it can't, becaue Agatha is still a historical personage and Wally a fictional one. It would take a completely fictionalized story to bring this incongruous match to a satisfying conclusion.

Nevertheless, Hoffman is so much fun coming on to the towering Redgrave that audiences may be willing to overlook the flat denouement. Wally, a cocksure little American who is having the time of his life outclassing his British publisher and British colleagues, possesses phenomenal self-assurance. Initially, you're tickled at his sheer presumption at approaching the tall, regal Agatha, but that presumption is eventually dignified by a genuine love.

Wally may be a breakthrough performance for Hoffman. After this witty, romantic characterization, it's difficult to imagine him slipping back into perpetually boyish vulnerability. Although he wasn't totally convincing as the heartless ex-con in "Straight Time," that difficult role may have pointed Hoffman in the direction of a versatile middle-aged career. After "Agatha" one can imagine him in Cagneyesque roles or as a dapper sleuth like Nick Charles. He seems to suggest an exciting new range of characterizations.

The height disparity between Hoffman and Redgrave is exploited with triumphant wit. For example, their first encounter, with Hoffman leaning down to whisper advice to Redgrave as she bends to line up a billiards shot, is sublimely echoed in a brief romantic interlude when Redgrave lowers her noble head, the neck arching with astonishing grace, to kiss her short but utterly composed suitor.

Timothy Dalton cuts an impressively virile figure of a different kind as Agatha's estranged husband. Looking startingly similar to Olvier at about the time of "Rebecca," Dalton creates an impression of an unfaithful husband that lacks neither sex appeal nor integrity. He's forthright about his alienated affections, more perceptive in his unkindness than Redgrave's wronged Agatha, who refuses to admit that their marriage has become a misalliance. Dalton and Hoffman seem to have developed a prickly rapport. Their encounters crackle with humorous tension, as the characters exchange politely hostile, suspicious vibrations.

In addition, the supporting cast is notable for vivid characterizations by Helen Morse as a cheerful young woman who befriends Agatha at Harrogate, Alan Badel as Wally's aristocratic publisher, Timothy West as a provincial policeman, Paul Brooke as a provincial journalist, Carolyn Pickles as Agatha's secretary and Yvonne Gilan as a Harrogate therapist. The plot of "Agatha" comes up short, but every other aspect is highly enjoyable, especially Hoffman's cunning demonstration that short can be irresistibly seductive.