Louis Malle was in his mid-fifties when he made the film he always knew he must make. It tells of his time as a young Catholic boy at a convent school in Nazi-occupied northern France and his friendship with one of the three Jewish boys the monks took in under assumed non-Jewish names in the hope of saving them. This was an act of Christian generosity, bravery and quite likely self-sacrifice. All too soon, after several searches by German soldiers and feral French collaborators that ended in failure, the three boys are betrayed and collared.

With the rest of the school assembled in the freezing yard looking on, they are led away and, with them, Father Jean, their would-be saviour. "Au revoir mon pere," chorus the Catholic boys to their headmaster. "Au revoir les enfants," replies Father Jean, "A bientot."

Then, by way of epilogue, we hear Malle himself: "More than 40 years have passed but I shall remember every moment of that January morning until the day I die." Au Revoir Les Enfants was released in 1987. By then, Malle had made more than 20 feature films and was a famous and lauded director in Europe and America. Why so late? "For years, I didn't want to deal with it. What happened was so appalling," he told the critic Philip French, "it was such a shock it took me several years to get over it, to try to understand it - and, of course, there was no way I could understand it. For 25 years, I wouldn't even talk about it. It's not that I wasn't thinking about it - it kept haunting me all these years but I wouldn't tell the story to anybody.''

Au Revoir Les Enfants, which is being re-released this month across Britain, is a wonderful film, once seen not easily forgotten. But so rich is it in detail, so subtle in the shooting and the telling that it repays a second or even a third viewing.

It is full of foreboding and it ends in tragedy but it offers so many pleasures. The feeling of the boarding school is brilliantly captured. You would be pushed to find a better account of the behaviour and interaction of young boys, the comic and cruel things they do together, their fun and their miseries; there is Father Jean, severe, august, saintly.

At the core of the story is the relationship between Julien (the Louis Malle character) and "Jean Bonnet" (a Jewish boy he discovers is really called Kippelstein). And the most detailed and nuanced scene of all: the lunch in a local restaurant involving an old Jewish man, French collaborationists, German officers, Julien, Kippelstein and Julien's glamorous upper-middle class mother (her lipstick is the only touch of red Malle allowed on to the film's muted palette).

The Jewish boys, as we read on the screen at the end of the film and as happened in reality, were taken to Auschwitz, where of course they died. Of the 38,206 Jews deported directly from Drancy, the Nazi internment camp near Paris, to Auschwitz in the course of the war, 779 survived but not a single child.

Father Jean, in real life Father Jacques, was taken to various concentration camps, finally to Mauthausen in Austria. There he remained, concealing his religious status so when other priests were moved to a less gruelling camp, he was the only priest left to minister to the many thousands who remained. He was still alive when the Americans liberated the camp but died in hospital soon afterwards. In 1985, Yad Vashem named him ''righteous among the nations."

The vast majority of films about the Holocaust were made by Jews. Au Revoir Les Enfants is different from all the others, not only in quality but also in tone. Though very well received, greatly praised and awarded major prizes, there were dissenting voices. It is devoid of sentimentality which is a virtue, though the trenchant American critic Pauline Kael found it too cool, the Malle character unengaging and the main Jewish boy too beautiful and talented. She saw that as manipulation.

Malle was a Catholic though not a devout one but he was witness not just to events that were a microcosm of one of the worst crimes in history, he also saw what true saintliness is.

The record of the French Catholic church's behaviour to Jews during the war is mixed at best. In the first years while Petain, leader of Vichy France, was introducing anti-Jewish laws not at the behest of the Germans but in the name of La Patrie, within the humiliated country he depicted as undermined by freemasons, communists and Jews (the last two often presented as intimately connected) the hierarchy kept silent. But after the transportation of foreign Jews in the Vichy zone and the Paris Velodrome round-up of July 1942 where more than 13,000 were corralled before being sent to Auschwitz, it changed.

The following month, Archbishop Saliege of Toulouse wrote to his parishioners: "The Jews are real men and women… they are our brothers and sisters… a Christian should not forget this." Petain contacted the Papal legate to complain about the letter. During the reminder of the war, thousands of nuns, monks and priests performed heroic acts of protection and kindness. Nevertheless, in 1997 the Catholic episcopate gathered at Drancy and stated: "We confess this fault. We implore God to forgive us and ask the Jewish people to hear this cry of repentance."

France under Napoleon was the first country to afford Jews full civil rights; it was also a cradle of modern antisemitism - Edouard Drumont's La France Juive was published in 1885; Captain Dreyfus was arrested in 1894 (this week in 1898, Zola's " J'accuse" letter was published). Since the war, French Jews have been subjected to many murderous outrages, as we have so recently been reminded. Even in "normal" times, many would echo this exchange from the film: "Are you scared?" Julien asks his Jewish friend. "All the time," he replies.

The release of Au Revoir Les Enfants in 1987 had special resonance because it coincided with the start of the trial of Klaus Barbie in Lyon, a case that held the French nation in its thrall. Its long-planned re-release comes in the month when French Jews are again are suffering the truth of the line in the Seder service: "in every generation they rise against us to destroy us."

'Au Revoir Les Enfants' will be released in cinemas later this month.www.bfi.org.uk/releases