FIELD OF BLOOD. By Gerald Seymour. Norton. 352 pp. $14.95.

THE title is biblical and refers to the ground bought with the 30 pieces of silver Judas earned for his act of betrayal. The Judas here is Sean Pius McAnally, who, unable to absent himself from the Protestant-Catholic bloodbath in Northern Ireland, turns informer, or, as he's called here, "tout" or "supergrass."

But the tout is a figure all, even the beneficiaries of the betrayal, despise. Indeed, though the British call McAnally a "Converted Terrorist," they, like their enemies, agree that the tout is "a dark shadow swimming as a germ in the bloodstream." McAnally loses everything, including the love of his wife, Roisin, his son, Gerald. Even his parents turn his photograph face down.

Yet McAnally had been brought back into the fray from his refuge "down South" unwillingly. It is clear that he remembers all too vividly what his marksmanship had wrought. He waits in a queue at a roadblock, for instance, and notes that the soldiers are "as young as the constable who had been killed in the flame-flash of the R.P.G. missile three years before, as young as the soldier blinded by a missile's shrapnel two years before."

Author Seymour styles this novel much the way someone drawing in charcoal might, with broad, bold strokes: "Blackened faces and hands. Rifles cocked, one up. Quiet padding feet. The glow of the image intensifier night sights carried by the marksmen . . . Always bloody raining, and the haze of mist cloud sneaking in from the fields at the foot of the mountain to blanket Turf Lodge. No street lights . . ."

The technique is especially apt here, somber as well as suggestive. When we close the book it is with a sense that the war in Northern Ireland has smudged every character, stained every page. LETTERS FROM THE DEAD. By Campbell Black. Villard. 227 pp. $15.95.

IN this occult novel we have two women, one divorced, one separated, vacationing with their adolescent kids in an isolated beach house. The kids find a Ouija board and, too hesitantly to be believed, begin to play around with it.

Then Strange Things happen, but not the sort we need in a novel that is to scare us. There are messages, natch, and then there's the fact that Tommy's closet door won't stay shut. One character will see a figure that no one else sees. But big deal! These are lukewarm events, none with any aerobic effect.

A writer might get away with this if we cared for the characters. Here they are so lacklusterly drawn that we can't muster even concern much less the heart-pounding, short-of-breath terror that we hope to feel.

And the ending! But at least the book does end.

A stylistic quibble must be made, to wit, that author Black is so enamored of vers libre that he attempts to fill this novel with it.

"It didn't seem to help.

Martha looked at the kid's face.

Wherever she was, she wasn't in this bedroom.

She was absent.

The eyes were lifeless.

An absence of light in the pupils.

Dead eyes."

Perhaps Black thought this technique would give his listless book a boost. Alas, it didn't.

THE ALCHEMIST By Kenneth Goddard Bantam. 405 pp. $14.95

THIS cleverly plotted novel takes us into the wonderful world of designer drugs. In this case, the excitement centers around a goodie called Rainbow Vision. The drug's very legality threatens to destroy a carefully cantilevered network of bosses, distributors, and dealers as well as a government undercover operation that is in place to nab cocaine traffickers.

There's a lot of gory infighting and skullduggery, but of an imaginative sort. One of the villains, for instance, the overweight Simon Drobeck, is always accompanied by his pet python. Drobeck's methods of revenge are slithery and not at all upscale. Similarly, there's the pimply Eugene Bylighter, who provides an abundance of comic relief.

Things happen and scenes shift at breakneck speed. Goddard writes this sort of thriller so smoothly that even his shortcuts, which have a curious Anglo-Saxon ring to them, work. He'll talk of someone's "alley-parked car" or "blood-spurting body" or "still-smoking pistol," for example.

There is nothing like nuance here; what you see is what you get, but what you get is plenty. ? DARK GODS. By T.E.D. Klein. Viking. 259 pp. $16.95.

THE Library of Congress catalogues this collection of four stories as "Horror tales, American," and, while they are that, they are also more than that categorization implies.

For one thing, Klein is a real writer, one who transcends genre. His settings seem incredibly detailed, although, upon examination, they turn out to be done with but a few strokes. This is as true of his shabby bungalows in a retirement community in Florida as it is of his Upper West Side New York or his oceanside boardwalk. Even a laundry room is more than a laundry room, true and energetic and alive: "The dryer regarded me silently with its great cyclopean eye. The fluorescent lights buzzed louder. On the wall someone had scratched a crude five- pointed shape . . ."

And the same must be said about Klein's ability to portray character, in dialogue and in description but also in the equally difficult matter of observation. When he tells us, "George's embarrassment embarrassed them all," we see the scene, recognize it, know exactly what he means.

But over and above that, Klein's stuff is scary in a deep, resonant kind of way; what he writes about is not horror, but dread. THE KREMLIN CONSPIRACY. By E. Howard Hunt. Stein & Day. 336 pp.$15.95.

THE TITLE has a real old-fashioned ring to it, and the contents do, too. Take for instance the references to "peaceniks." Still, this novel is fun to read because it's as formulaic a "man's" book as a romance is a "woman's" book.

In a romance, readers want to know what the heroine is wearing. In a genre spy thriller, they ask what sort of weapon the hero is packing. In this book there are Walthers and Birettas and a .9 mm Steyr automatics as well as coshes which, for those not in the know, are similar to blackjacks.

In this book, too, there's that Maleness, that comradeship that literary critic Leslie Fiedler got famous identifying. In this version, the good guys sauna together and have at each other with birch switches. The bad guy, on the other hand, is into flagellation big time, and who but a raven-tressed lady (another Fiedler favorite) should wield the whip.

There are disguises aplenty, and some acid (again, the old- fashioned corrosive kind) is slipped into someone's aftershave.

My favorite passage, a threat, is worth quoting: "From his boot he pulled a knife, tested the edge with his thumb. 'Noses don't replace themselves.' "

In this case, the character's response mirrored the reviewer's own: "She shivered."