SUMMER READING ISSUE : Vive La France : FICTION : THE WORLD AT NIGHT,<i> By Alan Furst (Random House: $23; 257 pp.)</i>

Like the phosphorescent wake of a night swimmer, the thriller plot of “The World at Night” lights up the dark element it moves through, in this case the national agony and moral cloudiness of occupied France in World War II.

Alan Furst’s story of Jean Casson, a second-rate movie producer who temporizes, hesitates and stumbles into valor, earns a comparison with the serious entertainments of Graham Greene and John Le Carre. The action, with agents and double agents, collaborators, resisters, opportunists and a beautiful, pain-etched heroine, is taut and melodramatic.

It is a vehicle and it is easy to imagine a movie that would recall--apologies for still another comparison--”Casablanca.” But it is a vehicle notable not just for its dash and cornering, but also for what it carries. Using the pleasurable devices of its genre, it offers a lot more: an appreciation of France that is at once passionate, graceful and cold, an evocation of French virtues and vices under terrible testing, and a shrewd intuition of the peculiar national way in which it was terrible.

Casson had a preliminary twinge. Mobilized to film the exploits of the French army, he is ignominiously demobilized in a cow pasture when his camera truck is blown up. In the unprepared chaos of a bombardment, he had seen a grossly fat French general struggle from his car to insist that the incoming shells were an error by the damned Brits, not a German attack, and to refuse to allow the French guns to reply.

Joining the choked tide of soldiers and civilians fleeing the blitzkrieg, Casson sees a staff car bulling through to safety, “packed with senior officers, faces rigid, sitting at attention while the driver pounded on the horn and swore.” Beside him straggles an old man, a painter from Brittany.

“We’ll all live deep down now,” he tells Casson. “Twenty ways to prepare crayfish. Or, you know, chess. Sanskrit poetry. It will hurt like hell, sonny, you’ll see.”

The midnight of the title is that hurt: the darkness not of war but of the deceptive and self-deceiving aftermath of defeat. The Germans were ambivalent: On the one hand they wanted to humiliate France; on the other hand they wanted to preserve enough of it to dominate and enjoy.

Vichy, south of the Loire, was allowed semi-independence for a while under the ultra-right regime of Marshal Petain. In Paris and the rest of occupied France, many of the French tried in the first years to come to at least passive terms with force and confiscation. The Germans courted a few groups: businessmen, intellectuals, artists. Some collaborated actively, some profiteered; others did well or poorly along a whole diapason of conscience and expediency.

Back in Paris, his production company at a standstill, Casson consults a friend who manufactures lightbulbs, which the Germans buy in great quantities. It is his trade, he explains, just as a barber’s is to cut hair, German or otherwise. And it is Casson’s trade to make films. But will he be able to make what he wants? he asks. Was he ever able to? the friend demands. Hunker down, is the message. “Your life is your country now, my friend.”

The beauty of Furst’s book is Casson’s effort to put the phrase to work, what he finds among others who attempt it, and how it eventually fails. His divorced wife moves among a prosperous circle of people who do a little business with the Germans, arguing all the while that business and private life are separate. The day comes when she turns to Casson in despair: Her lover has brought home a corrupt German officer with whom he conducts a trade in confiscated cars.

Casson is courted by a German film executive whom he had known before the war. Germany wants French films and there is plenty of room to work between pro-Nazi propaganda and political subversion, this sensitive, highly sympathetic German argues. He takes Casson to excellent lunches that few French can afford; he provides seed capital. A Jewish screenwriter produces a beautiful romantic script and Casson pays him and presents it under a pseudonym.

It is no use; life cannot be a country if there is no country. In a gripping, beautifully detailed sequence, the still ambiguous Casson goes to Spain, ostensibly to scout sites--in fact, for British intelligence. It is a disaster that gives an absorbing glimpse into the moral maze of espionage. Casson returns to try to go on with his film work and to pursue Citrine, an actress who is an old love.

An ingeniously portrayed German intelligence agent blackmails him and sets him up as a double agent. Casson, condemned to heroism, turns double agentry to triple agentry. After some excessively melodramatic twists--the only time when Furst overdoes it--there is an ending whose ambiguity amplifies what has gone before instead of shutting it down.

There is a lot to amplify. Furst has a splendid feeling for moods, gestures, landscapes and the sweet and acrid aspects of France. The moral desolation of occupied Paris is tangible: the vile graffiti of German uniforms against that great wall of history, the Seine embankment; the fury of a French waiter serving ersatz coffee. The French prize order, beauty and small things done well. Surfaces, if you want to call them that, are a religion; that waiter was forced into propagating not just bad coffee but blasphemy.

Furst writes of a series of one-night stands, of women, some married, who sleep with Casson for warmth--a bitter winter and no coal--as well as a reminder of who they were when the world worked. The author gives each an intelligence, a spirit, a style as well as a body. The angles of each one’s limbs in bed trace the initial letter of a lucid sentence.

In the restaurant, Casson’s German associate orders fine wine, a reblochon cheese, pears. Here is the profound pain and humiliation of occupation. All the beautiful things that it was France’s genius to enjoy lie under a sign of corruption. The German’s effort to be reasonably decent: corrupted. The Seine with German soldiers: corrupted. In short, that wonderfully sensible and utterly useless phrase “Your life is your country”: corrupted.

The actress Citrine, a splendid haunting figure, recognizes it. When Casson tracks her down for his film, their old love kindles. She will not allow it. Casual sex is not for them and to admit love would invite the shadow that has blighted the pears, the reblochon and all the other beauty of France. It is a stance of formidable elan; later, of course--even as Casson moves toward engaging his life in hopes of restoring his country--it melts. The heart, as the French say, has its reasons that reason cannot touch. Furst does, though.