It is 1942 and Field Marshal Romel's tanks are blazing their way across the desert toward Alexandria and Cairo,while the British bumble and worry behind lines of defense that seem to melt whenever a swastika comes into view.

In the native sections of Cairo, a group of Egyptian army officers, led by a 22-year-old captian named Anwar el-Sadat, is trying to contact Rommel with a plan to stage a rebellion, help the Germans to victory and establish a government of Egypt by and for Egyptians. It is a race against time; if they don't get their proposition to Rommel while he still can use some help, they will have no bargaining leverage.

The key to both efforts is a German spy enigmatically code-named "Sphinx," who has managed to slip into Cario, get access to British battle plans and radio them out to Rommel regularly, using a code based on Daphne du Maurier's novel "Rebecca." Having tried to contact Rommel by flying in a courier, who was promptly shot down in flames by the Germans, Sadat would like to borrow the radio and the code for a little, chat about the future of Egypt. The British would like to find the radio and its operator for reasons of their own.

Against this background, Ken Follett (who is probably best known for an earlier thriller, "Eye of the Needle") has woven an intricate story of violence, intrigue and exotic passions that compares curiously with current trends in action-suspense fiction. "The Key to Rebecca" is a novel primarily in the post-Helen MacInnes school, rather than the post-Ian Fleming school that has set the trend for a decade or more. tIt will impress readers in the 1980s as comfortably old-fashioned -- or uncomfortably, depending on taste. Its characters and action are, on the whole, slower-moving, less chrome-hard and glittery, not quite so eccentric or one-dimensional. But in their pre-jet-set way, half a dozen of the characters are quite vivid.

The book also offers some fine descriptions of life in Egypt during the war, and a plot with many twists -- perhaps a few too many in the last 100-odd pages, are the cornered spy keeps escaping miraculously from traps that should work. One finally begins to suspect that the author wants to prolong the book to an arbitrarily chosen length, or that he has simply refused to sacrifice a few pet scenes that don't quite fit in the final product -- particularly the one in which the spy holds a woman and child hostage during an eight-hour train journey.

Despite its old-fashioned flavor, which is appropriate to the time and place of the action. "The Key to Rebecca" has some contemporary touches: a kinky scene of sex a trois, for example, and several episodes that seem to have been written with movie options in mind. One is a splendidly elaborate riot staged in the streets of Cairo as background for the snatching of a document-loaded British Army briefcase. Another is a chase scene, in which the spy, fleeing on foot but armed with a knife, is pursued (through alleys, up and down stairs) by an officer who is riding a motorcycle but unarmed. The same sturdy motorcycle, recovered from its stair-climbing experiences, later chases a train that is carrying the spy and his hostages. And at one point, it follows the spy out to a scene at the pyramids by moonlight, which may have been put in only because Follett wanted to do a scene at the pyramids by moonlight.

Some traces of the Ian Fleming style can be found in the character of the villian: Abwehr master spy Alex Wolff, alias Achmed Rahmha, who is a cold, efficient killer, a man of the world addicted to champagne, caviar and beautiful women, totally dedicated to the simple idea that the world is divided into two kinds of people, slaves and masters, and an expert at languages and disguise able to pass for an Arab or an officer in the British Army.

Pitted against him is British Major William Vandam, who seems borrowed from a Le Carre novel: an aging, harassed intelligence officer who has as many problems with his superior, the supercilious, Machiavellian Lt. Col. Reggie Bogge, as he has with the enemy. Counterparts of the villain and hero are hero are the women they use as bait: Sonja, a voluptuous belly dancer who hates the English; Elene, who is Jewish and decides to try espionage because she sees no promising future in being a kept woman.

Vandamhs hunt for Wolff, while Wolff is tracking down and relaying British military secrets, is presented against a colorful, vividly described background in a plot that is only a little bit too intricate. Follett has produced a book that will keep readers turning the pages -- though the tempo may slow down a bit near the end, when it should be at its most intense.