Few films in the history of cinema can claim to have had a direct impact on the real world. A movie showing in France has managed to repair a half-century of injustice even before it appeared on general release. Indigènes tells the largely concealed story of the 300,000 Arab and north African soldiers who helped to liberate France in 1944.

In one respect, the film has already succeeded where years of complaints have failed. Last week, just before it reached the cinema, the French government was shamed into paying belated full pensions to 80,000 surviving ex-colonial soldiers who, since 1959, have been paid a fraction of what French veterans receive. The movie has more ambitious, political aims. Its director, Rachid Bouchareb, and its co-producer, Jamel Debbouze, hope that it will be an important turning point in race relations in France. It is a big hope.

M. Debbouze, 31, is France's best-known citizen of north African origin, other than the footballer Zinedine Zidane. He is mostly known outside France as the shy grocer's boy in the hugely successful Amélie (2001).

Both M. Debbouze (French-born of Moroccan descent) and M. Bouchareb (French-born of Algerian descent) hope the film will remind the majority population of France that the country owes a deliberately obscured debt of blood to colonial soldiers with brown and black skins. They also hope the film will persuade young French people of African origin that they belong in France.

M. Bouchareb and M. Debbouze took the film on a pre-release tour of France's multi-racial suburbs last month. Almost a year ago, the same suburbs exploded into a frenzy of car-burning and destruction of public buildings.

M. Debbouze told the mostly young, mostly brown and black audiences that it was time that they understood that "France's story is your story. You have a right to be in this country, whether you are black, brown or yellow".

"Our great-grandfathers liberated France. Our grandfathers reconstructed France. Our fathers and mothers cleaned France," he quipped. "It is time that our generation told the whole story."

The story of the "indigènes" (natives) is indeed worth telling. More than half the French "liberation" army of 1943-44, which fought in Italy and France, was of African origin. There were 550,000 men in the French army in 1944. Mostly, they were recruited in the unconquered French African colonies. Of these (leaving aside colonists of French origin), there were 134,000 Algerians, 73,000 Moroccans, 26,000 Tunisians and 92,000 men from colonies in black Africa.

This multi-racial army was first thrown into battle in Italy in 1943, in the grim struggle to dislodge the Germans from their fortifications at Monte Cassino. The same troops landed with American troops in the south of France on 15 August 1944, while the main German occupying force was engaged in Normandy. After advancing through France, the southern invasion force became involved in terrible winter fighting against the German armies which had assembled to defend the approaches to the Reich in the Vosges mountains and in Alsace in northeastern France from December 1944.

The movie follows the boot-steps of four north African soldiers, played by M. Debbouze, Samy Naceri ( Taxi), Roschdy Zem and Sami Bouajila. Bernard Blancan plays a "pied-noir", or white Algerian colonist, sergeant, who is revealed - to his fury - to be half-Arab. The five men shared the male actor's prize when the movie was shown at the Cannes film festival in May. The story is loosely based on the actual history of the colonial "tirrailleurs", or soldiers who volunteered, or were coerced, into saving a "patrie" (homeland) they had never seen. M. Bouchareb spent two years gathering information and anecdotes from survivors. Many incidents in the movie are based on real events. There is a mini-riot when the colonial soldiers are told that tomatoes are reserved for the whites. Army censors intercept and destroy mail to break up relationships between Arab or African soldiers and white women. The French army refuses to promote Arabs and blacks above the rank of corporal.

The movie ends with a battle in a half-ruined Alsatian village between Germans and a handful of north Africans, disillusioned but determined to fight, at least for their friends. This, too, is based on a real battle in December 1944, just before the Battle of the Bulge, a little to the north.

Other aspects of the movie have been disputed by historians. Indigènes suggests, for instance, that colonial soldiers were regarded as expendable. Although the African troops were thrown into murderous battles, there is no clear evidence that they were singled out as cannon fodder.

Benjamin Stora, a French historian who specialises in the late colonial period, said: "In some ways the army was less racist than colonial France. Blood sacrifice and the fraternity of combat were taken seriously. Native troops were not pushed systematically into the front-line. There were even mixed-race regiments."

In other words all soldiers, not just the brown and black ones, were regarded as expendable. The fact remains that the "French" army of 1944 was more than half African or Arab. It was therefore inevitable that the "tirrailleurs" and other colonial soldiers would suffer disproportionate losses. One quarter of all the French soldiers who died in the 1939-45 war - 60,000 men - were from France's "African legion". About 10,000 of these casualties were white colonists. The rest were brown or black.

The real scandal is that the role of the brown and black troops was deliberately disguised at the time and has largely been airbrushed from French history. Contemporary newspaper pictures and newsreel footage - as hinted in the film - showed French conquering troops as white. The "natives" were literally kept out of the picture.

This was partly unthinking racism; partly political calculation.

In 1944, General de Gaulle was building a case that France was not a liberated victim of Nazi conquest but one of the "victors" of the war and still a great nation. He needed to persuade the other allies, but most of all the French people, that France had played a large part in its own liberation.

Official French memory of the war has not concealed the role of the American and British and other troops who invaded France in 1944. It has exaggerated the role of the French resistance movements and it has played down, or even ignored, the fact that many of the French troops in 1944 were of Arab or black origin.

The greatest virtue of the film is to bring these facts before the wider French public for the first time.

The film is doing well at the box-office. In its first two weeks, 1.5 million people in France saw Indigènes. It has, however, been notably more popular in the multi-racial suburbs than in mostly well-off and white Paris.

The French President Jacques Chirac was given an advance showing early last month. He promised to respond to the film's protest - in a written message at the end - about the frozen pensions of colonial soldiers.

M. Bouchareb said his intention in revisiting the forgotten history of 1943-44 was to ease, rather than to inflame, racial tensions in France. By telling the real story, he says, the presence of African communities in France is placed in a new perspective. "Despite their many rejections, despite the unpaid pensions, the veterans have no spirit of hatred," he said. "They remember the fact that they were applauded as they marched through French villages. I wanted to make this film for a long time so that young people, especially in the suburbs, would know that, and so that older people of all races would remember it. It has come just at the right time [after last year's riots]. It will lay a foundation stone on which we can continue to build."

Maybe. Many of the most bitter divisions in French society since the war have been based on a partial telling, or distortion, of what happened in 1939-45. Since the 1970s, there has been a slow process of facing the facts, from the active role of the collaborationist Vichy government in the persecution of Jews to the limited and belated (if real) contribution of the resistance movements.

Is France ready to acknowledge its debt of blood to Arabs and blacks? The detailed coverage of Indigènes in the French press suggests it could be. The relatively modest success of the movie, especially in white, middle-class Paris, may tell another story.