The Fox and the Spy : CITY OF GOLD <i> By Len Deighton (HarperCollins: $20; 368 pp.) </i>

January, 1942; the North African campaign of early World War II. Gen. Erwin Rommel, the fabled “Desert Fox,” has thrown the British Army back 300 miles in 17 days, moving within a sandbox of Cairo. It’s almost as if Rommel knows every Allied move in advance.

He does.

Len Deighton to the rescue. Deighton sends Maj. Bert Cutler, more recently a Glasgow detective, by train to root out the spy. Doing double-duty, Cutler also is escorting under arms a prisoner, Cpl. Jimmy Ross, coincidentally another Scot. Ross has whacked his commanding officer, who’d “had it coming.”

The major has a fatal heart attack on the train. The corporal swaps identities, lifting Cutler’s pink ID tag of the SIB--Special Investigation Branch--a kind of military carte rose allowing the holder to represent himself any way he chooses, even as a corporal.

Now there’s a premise: a plucky Highland lad, wanted for murder, impersonating an officer, turned loose in the slumgullion of wartime Cairo to catch a spy in whose hands rests the outcome of the century’s most wrenching upheaval.

Or will he just split? Nah. Ross considers it, of course; with his stolen SIB card he can be most anywhere in as short a time as it takes to get there. But then he meets Alice Stanhope, whose beauty rivals that of Cleopatra, or at least Greer Garson . . . Besides, this is a Deighton story, and as such, well worth hanging around for, right? Not necessarily.

In the finest Deighton form--from “The Ipcress File” through “Spy Sinker”--the master sets up his row of people, then surrounds them with the authentic sights, sounds, smells, the moods and mores of their locale.

Chapter 1, then, gives flesh to Ross and the star-crossed Cutler. Chapter 2 presents fleshy, arrogant Sergeant Smith and brutal, Teutonic Sergeant Percy in a rendezvous of ill intent in El Birkeh, Cairo’s “pleasure district”--more specifically in Lady Fitz’s place. (Deighton doesn’t just describe a whorehouse; he brings you there and closes the door.) In Chapter 3, Peggy West, a nursing sister, visits Solomon al-Masri on his Nile houseboat City of Gold to pick up her monthly remittance from husband Karl, off somewhere doing something she’d rather not know about.

Again in the best tradition, their fates are entwined, while Cairo insinuates itself as co-protagonist: “Other cities smelled of beer or garlic or stale tobacco. Cairo’s . . . was a more intriguing mix: jasmine flowers, spices, sewage, burning charcoal and desert mist . . . A golden beehive frantically active, dribbling with honey, always ready with a thousand stings . . . A zigzagging maze of medieval alleys. The oldest surviving city in the world.” A labyrinth indeed--where, at length, Deighton himself gets a little disoriented.

Maybe the time and place are too Byzantine even for a spy novel. As one of Deighton’s many extras--brassy American newsman Harry Weschler--notes, “There is a big story here: Arab nationalism, British colonialism, the Jewish homeland and Nazi expansionism. Everybody fighting everybody”--and Deighton trying to extract a little myrrh from every faction.

Maybe, too, it’s Deighton’s unfamiliar obligation to play by the rules. On his copyrighted Cold War turf, the finale was still in the balance. The outcome of the North African Campaign is solidly in the history books. (Was Rommel really getting tipped off to “every last detail down to the mobile bath and delousing units”? Absolutely. Did the Nazis use the information to take dead aim at British Cairo? To be sure. Did Rommel invade the city? Shame on you.)

Nevertheless, with knowledge aforethought, Deighton pushes on, serving up some delicious red herrings en route. There is Wallingford, a bogus British naval officer who, with a band of odious confreres, is running guns and and other “salvage” from the desert battlefield. (How does he know the precise location of a huge cache of Italian submachine guns?) There is Prince Piotr, a White Russian and putative crony of King Farouk (who also makes the scene, nightclub-hopping in a red Rolls with a convoy of infantry).

There is Capt. Robin Darymple, who gets zonked on a hubbly-bubbly of hashish and sells his soul to an unctuous banker named Mahmoud. And there is the customary ration of public-school pals, the ones who call each other Piggy and Bunny and refer to ferocious battles as “our little show.”

Alas, with so many characters in such close quarters, we’re left with more loose ends than an $8 haircut. Happily there are enough Deighton touches to make it all almost worthwhile:

Mahmoud sports “a white mustache that fitted across his dark face like a strip of adhesive tape.” A German, asked “What is it you chaps do in Krautland when you’re happy?” replies, “We invade somewhere.” A pompous British Brigadier (which may be redundant) nutshells his entire grasp of religion: “Saint Paul was a Jew too. He was a Pharisee: that’s a select school of Judaism. Paul was a disciple of Rabbi Gamaliel, an important Jewish leader. Apparently it was this fellow Paul who created the whole Christian business: the whole rigamarole . . . “

In the end, though, Deighton weaves in and out like a game old champion boxer who’s misplaced his skill but fights splendidly each round for one minute out of three.

In the end, Peggy West, inheriting Solomon’s houseboat, rechristens it City of Brass. Hear-hear.