THE JUDAS FACTOR By Ted Allbeury Mysterious Press. 201 pp. $15.95

ONE OF these days some scholar, possibly in a German university where the study of spy fiction is taken seriously, is going to tell us why Ted Allbeury, one of the best writers of spy novels in the business, well regarded in Britain and translated into 15 languages, remains so little known in the United States. Over the long haul -- The Judas Factor is at least his 25th book -- Allbeury is arguably the best teller of spy tales to come out of that growing group of authors who once were spies themselves, and I include John le Carre' in that judgment. Yet he remains relatively unread here, and indeed is so little remarked upon that Anthony Masters, in his recent book on writers who worked as spies (Literary Agents: The Novelist as Spy) finds no room to mention his fellow countryman even once, despite making space for such dubious writers as Tom Driberg and romanticizers like Ian Fleming. Why?

The problem may be that Allbeury pretty much tells it as it is: he was there, and he knows what it feels like to lie to a man, to walk the streets of Addis Ababa in a cold sweat, to be bored in Berlin. His books tend to be sad in tone, for spying and betraying and manipulating weak people into becoming even weaker is rather sad work. He does not think in terms of black and white: the protagonists in The Judas Factor, one working free lance for British intelligence, the other a professional assassin for the KGB, are both shown in a sympathetic light, though both can be cruel, weak in their own ways and even incompetent. Reality such as this can scarcely please the avid cold warrior or the reader who expects all heroes to perform to the perfection of James Bond. Nor is there much sex in Allbeury's books, or at least not more than there is in real life.

The Judas Factor is a representative Allbeury product. The plot is tight, the writing is spare, and the conclusion has the bittersweet irony at which the early Graham Greene and the late Francis Clifford were once so good. Allbeury shows us the professional assassin at work, a married man with a loving wife and child, a man who is good at his job and has only momentary doubts about its legitimacy. British intelligence decides it would like to kidnap the KGB agent, Vasili Burinski, and sends in Tad Anders, once employed by Secret Intelligence, now kept on a leash by having had his seedy though agreeable Soho nightclub paid for him by MI6. Preparation is too quick and too careless and the operation is busted. Or was Anders betrayed?

Allbeury is strong on characterization. He gives us real people doing real things. I have read 17 of his books, and I have no trouble keeping them apart in my mind, for he does not rely on repetitive car chases, torture scenes, kinky sex, descriptions of mechanical wonders, cataclysmic countdowns or excessive tradecraft to keep his story moving. He writes quiet page-turners that can be put down and that will always be taken up again, because one comes to care about the people. In The Judas Factor there are several secondary figures that interest us: Tad's two girl friends and the working-class mother of one and the toffee-nosed parents of the other; Burinski's wife; Ander's partner in the Berlin operation; the men in British intelligence to whom he is to report. Each occupies space that is his or her own; these characters are not interchangable parts.

JUST HOW GOOD is Ted Allbeury? Perhaps he has produced too many books: those 25 or more have all been written since 1970, when he began his first, A Choice of Enemies. Though his characters are not interchangable, at times his moods are, for his concern with subtle moral betrayals is almost elegaic and binds most of the novels together in a common tone. Perhaps his books are too authentic for readers who believe that entertainment and escape are synonomous. Perhaps he is not quite cynical enough for readers who want to think the worst of themselves or their countries, since most of Allbeury's figures are reasonably decent people. And though he can be sympathetic to those who come from eastern Europe or the Soviet Union, he still clearly believes in Western values. I would have said that Allbeury is very good, a steady, often compelling, always interesting writer, more than a journeyman, more than merely dependable, though perhaps lacking that distinctive mark that has led le Carre', Len Deighton and others to such grander successes. But of those writers of spy novels who blend fiction with a firm grounding in reality, there are two who stand above the others, because both have been there: Charles McCarry, formerly of the CIA, and Ted Allbeury, formerly of SIS.

Of course, spy fiction doesn't do as well as mystery fiction, by and large, just as few spy series last long on television, while Miami Vice, L.A. Law, and their like thrive. Spying is claustrophobic, not cinematic. We all can relate to the detective story: we recognize the streets of San Francisco and the squad car and we all have seen a policeman. Allbeury's special skill is to convince us that we have all met a spy or two as well; we simply didn't know it.

Robin W. Winks teaches history at Yale University and frequently reviews mystery and spy fiction. His most recent book is "Cloak and Gown: Scholars in the Secret War."