HAWKSMOOR. By Peter Ackroyd. Harper & Row. 217 pp. $16.95.

HAWKSMOOR, a novel by Peter Ackroyd, highly acclaimed British author of a recent biography of T.S. Eliot and the fictional Last Testament of Oscar Wilde, may leave many readers baffled. Is it a work of literature in which masterly style and philosophical inquiry are united? A beautifully and skillfully written story of the supernatural? An entertaining mystery rich in atmosphere and detail? Maybe it is all of these.

Hawksmoor interweaves two stories, one being confided to us in the intimate first person by Nicholas Dyer, an 18th-century architect commissioned in 1711 to design seven London churches under the direction of Sir Christopher Wren. The other story is a third-person account of a series of murders being committed in present-day London in or near these very churches, and of the Scotland Yard detective Nicholas Hawskmoor who is trying to solve the crimes.

Dyer's tale is passionate, full of eccentric and thought-provoking observations. His old fashioned English with its unfamiliar spelling and syntax seems at first forbidding, yet the rhythm of his sentences is so seductive that it soon carries us effortlessly along; and once he begins to tell his life story -- describing the Black Plague, the Great London Fire, his initiation into a mysterious demonic cult -- the narrative positively sings.

The contemporary chapters are cooler, more cerebral, but no less engaging as even the smallest characters are drawn with delicate psychological insight, the smallest scenes carefully described. The modern London of random children, indigents, the somewhat isolated and brooding Hawskmoor, is as fully realized in chilly colors as Dyer's dazzling past. The mood of the whole is sinister, almost nihilistic, dark without the promise of relief.

Dyer, our dedicated philosopher and architect, is a closet heretic secretly consecrating his seven London churches with human blood sacrifice to ancient demonic gods. He is a secret outcast in the new Age of Reason, obsessed with magic, with powers that defy reasonable explanation, with the riddles posed by Stonehenge and other scattered ruins that lie deep beneath the Christian edifices of his time. Hawksmoor's 20th-century murderer, we soon discover, is following the pattern of Dyer's sacrifices -- even the names and sometimes the circumstances of the victims are the same -- and Hawksmoor, sensing a pattern and struggling to comprehend it, is being driven slowly mad.

THE NOVEL cannot be read carelessly. The fabric is as dense as that of a poem. Switching back and forth between 1711 and the present, we find ourselves enmeshed in repeated words, questions, gestures as well as places and names. Bits of conversation, phrases, expressions of ideas appear first in one time, then in the other. And often the narrator or the characters appear to be commenting not only upon art, life, metaphysics, history, but upon the nature of the novel itself.

Witness Hawksmoor contemplating the latest unsolved murder: "All these events were random and yet connected, part of a pattern so large that it remained inexplicable. He might, then, have to invent a past from the evidence available -- and, in that case, would not the future also be an invention? It was as if he were staring at one of those puzzle drawings in which foreground and background create entirely different images: you could not look at such a thing for long."

Or Nicholas Dyer in a dialogue in a pub which he has set for us like an 18th-century play. "If I were a Writer now, I would wish to thicken the water of my Discourse so that it was no longer easy or familiar. I would chuse a huge lushious Style!"

The whole is too deliciously clever really to be justly described here. It is reminiscent of the recent film, The Draughtsman's Contract, and even reminds me a little of Virginia Woolf's Mrs. Dalloway, though it is entirely different in spirit and mood. It is a book for those who live language and the imagination; it is as intriguing as it is difficult, as entertaining as it is frustrating, as absorbing as it is opaque.

But is it satisfying? For me, there was no big finish in which a great coherent pattern could finally be discerned in the tapestry. No transcendent illumination of the story on any or all of its levels ever came. Many readers may be left wondering what to think of Dyer's cosmology, of his accomplishment within the novel, of the meaning of the very last pages, of all the philosophical and artistic questions raised throughout the work.

A bit of research indicates that it was a Nicholas Hawksmoor who was commissioned in 1711 to build six London churches. But how much difference should this make in our ability to unravel the book's mysteries when the general reader might never discover such a fact?

Whatever the case, the talent of Peter Ackroyd is dazzling. I suspect I'll be thinking about Hawksmoor for some time.