A Poet on the Prowl : DEVICES AND DESIRES <i> by P.D. James (Alfred A. Knopf: $19.95; 435 pp.)</i>

Phyllis Dorothy White James can now safely be called the pre-eminent English writer of mysteries. “Devices and Desires” is a main selection of the Book-of-the-Month Club, as was her previous book, “A Taste for Death.” It will have a first cloth printing of 175,000 and a Quality Paperback Book Club edition to follow.

Her books, like those of John Le Carre there and Tony Hillerman and Elmore Leonard here, have slipped the comfortable bonds of genre to reach far wider audiences, helped by the television dramatizations of some of her earlier books such as “Death of an Expert Witness.”

She is not the heiress-apparent to Dame Agatha Christie and reportedly does not enjoy being thought such. Christie’s ingeniously improbable plottings are not James’ forte, and commercially, Christie, the reprint rights to whose works changed hands a couple of years ago for $92 million, remains in a class by herself.

James is her own voice, creating her own tradition. Her writing does have echoes of a longer, Victorian tradition: the spacious novel with its loving attention to environments and atmospheres, the delineation of character (which Christie tended to skim over with telegraphic speed) and the conveying of nuance in relationships and moments. “Devices and Desires” is a comfortably spacious 424 pages long, as tidy and well-furnished as a Victorian parlor.

Her continuing protagonist, the poet-detective Adam Dalgliesh, a sensitive loner touched with sadness, has brought out a new, slim volume of verse and, resisting his publisher’s desire to push it like a candy bar, has retreated to the Norfolk coast to compose his soul in a converted windmill he has inherited, with a sizable sum of money, from a beloved, bird-watching aunt.

James’ descriptions of the Norfolk coastline in its remote, spare beauty, quite unlike the overdeveloped littoral elsewhere, appears to be born of close familiarity and abiding love. It is lovely to read about.

Dalgliesh’s only chore is to deliver proofs of a cookbook to its local author. It is enough to embroil him reluctantly in the local scene. The author is the sister of a man who directs a nuclear-power station near the sea. The station is under a publicity assault generated by an earnest, penniless young man who lives nearby and is sheltering a homeless mother and child.

A serial killer of young women, whom the media has named the Whistler, is stalking the vicinity (James is very good at evoking the horror of the confrontations) and Dalgliesh is sought out by a former London colleague who now heads the local CID and who regards Dalgliesh with a mixture of respect and scarcely muted resentment. (James is very, very good at the shoals and cross-currents of relationships.)

The large dramatis personae includes the director’s ambitious assistant, whom he is attempting to phase out as his mistress, too; a retired clergyman, his wife and the nice young woman who looks out for them; a free-spirited painter attempting, with the help of a beguiling and precocious daughter, to care for his motherless brood; and various boffins and stenos from the power-plant staff.

The director’s assistant is murdered, seemingly the latest victim of the Whistler. But it turns out that the Whistler had been nabbed not long before the killing, and a key question is: Who knew, Who didn’t? Even Dalgliesh is at least briefly a suspect; the victim was found at the shore, not far from the windmill. (“I suspect everyone . . . and no one,” a sleuth once remarked.)

As Greyhound used to say, getting there (in this case to the solution) is half the fun. In “Designs and Desires,” as in many mysteries, it is substantially more than half the fun. It is an irony particularly applicable to James that the more extensive the scene-settings and the more (Henry) Jamesian the characterizations, the more rickety and anti-climactic the denouement can seem.

The detecting of who did in the assistant is intricate and professional, and although it mounts to what used to be called a sock finish (and fiery as well), it also feels oddly perfunctory, like a grand opera built around a visit to Disneyland.

As if she were aware that the atmospheres (even the evidence of careful research about the perils and controversies attending nuclear power) were not enough, James has attached a subplot, involving a pair of minor-league terrorists at the plant, that is arbitrary and owes more to the work of Alistair MacLean, say, than to her own sensitive interpretations of present society.

She is not a poet of the abnormal, like her nearest rival, Ruth Rendell, who peers into the darkest recesses of the aberrant psyche as no one else does. But James is in her own right a poet of, perhaps, more universal men and women and especially those whose lives are touched with crime and death.

This is James on Terry Rickards, Dalgliesh’s touchy colleague: “Dalgliesh thought of him as a type of police officer less common than formerly but still not rare; the conscientious and incorruptible detective of limited imagination and somewhat greater intelligence who had never supposed that the evil of the world should be condoned because it was frequently inexplicable and its perpetrators unfortunate.”

This is Dalgliesh--on the same page; Rickards’ wife is expecting momentarily--remembering his wife and son who died at childbirth: “His memory of her, which for years, a traitor to grief and their love, he had resolutely tried to suppress because the pain had seemed unbearable, had gradually been replaced by a boyish, romantic dream of gentleness and beauty now fixed forever beyond the depredation of time. His newborn son’s face he could still recall vividly and sometimes did in his dreams, that white unsullied look of sweet, knowledgeable contentment, as if, in a brief moment of life, he had seen and known all there was to know, seen it and rejected it.”

Passages of such eloquence and sensitivity are not frequently come upon in fiction anywhere, and they have earned James her rightful pre-eminence. In context, they suggest that crime fiction as such has no limits, only limitations.