The streets of Paris ask an insistent moral question, now more than half a century old but as pertinent as ever. On many street corners, small plaques commemorate those who faced up to Nazism: “Here died so-and-so, résistant de guerre.”

When I lived in Paris, I often pondered the question posed by these small memorials: what would I have done? Would I have done anything? Some Frenchmen and women actively collaborated during the war; many quietly acquiesced to protect themselves and their families. Those who chose to resist fascism did so in different ways: some secretly and discreetly, some with guns and actions, others with words. Those who spoke up, and out, were perhaps the bravest of all: the saints, and the martyrs.

Exactly 50 years after the death of Pope Pius XII, supporters of the wartime pontiff are demanding his beatification, the last step on the road to sainthood, reigniting a long-running battle over whether he did enough, early enough, to condemn the persecution of Jews.

The Yad Vashem Holocaust Museum in Israel carries a deliberately provocative depiction of the Pope's wartime role, including him among the “unjust”. Hardline supporters of Pius have tried to ram through the process of sainthood with little regard for Jewish sensitivities. Pius has been condemned as “Hitler's Pope” by some critics and lauded by Pope Benedict XVI as a great leader.

Times Archive, 1958: The Life of Pius XII

In some quarters the Pope was considered to view Nazi doctrines and deeds with too great detachment

For all the fury and posturing, the story is essentially about how one very powerful man responded to the most pressing moral question of the age. This is not some distant historical dispute among scholars. It is a defining issue that asks, just as insistently as those Paris plaques: what would you have done? Eugenio Pacelli, who became Pius XII in 1939 and reigned at the Vatican until 1958, was an extraordinary man: compassionate, pious and utterly dedicated to his faith. He was no anti-Semite; far from being a Nazi sympathiser, he loathed Hitler with righteous passion, considering him “an untrustworthy scoundrel and a fundamentally wicked person”.

In Pope Benedict's words, Pius “worked secretly and silently” to “avoid the worst and save the greatest number of Jews possible”. There could be no direct orders to intervene, since the Vatican was officially neutral, but thousands of Jews were saved thanks to the Catholic Church, hidden in churches or issued with false passports.

But set against all this is the silence of the Pope. By the end of 1942, Pius had learnt details of the Holocaust's ghastly progress from at least nine different countries. Hungarian, Danish and Bulgarian church leaders spoke out, yet Pius made no formal protest or condemnation. A single sentence in his 26-page Christmas message of 1942 lamented “persons who, for no fault of their own, sometimes only because of their nationality or race, have been consigned to death”. He made no specific mention of the Jews, Hitler or the genocide then under way.

Under mounting pressure to make a stand, Pius was privately appalled but publicly cautious, even equivocal. The British envoy to the Holy See was astonished that the Pope seemed more concerned with the possibility that Rome might be bombed than “Hitler's massacre of the Jewish race”. One Foreign Office memo described Pius XII as the “greatest moral coward of our age”.

That is unfair. Pius's silence came not from cowardice, but calculation, his perceived duty to his Church, and fear of provoking Hitler to even greater crimes, endangering non-Aryan Catholics and Catholicism itself. “No doubt a protest would have gained me the respect and praise of the civilised world. But it would have submitted the Jews to an even worse fate,” he reflected. “The Pope cannot speak. If he spoke, things would be worse.” But how, in December 1942 with the gas chambers and crematoriums working day and night, could things possibly have got any worse? The argument that a condemnation of Nazi brutality would have made that brutality worse is unprovable.

Even the most powerfully worded encyclical might have had little effect on the accelerating brutality of the Nazi high command, but it would have placed the Church firmly on the moral high ground, and might even have galvanised anti-Nazi feeling among German Catholics.

After the Liberation of Rome, Pius could have threatened senior Nazis with excommunication. After the war, he could have explained why, as a virtual prisoner within the Vatican, he had opted not to make a solemn formal protest against the greatest crime of all time. He did not, offering neither regrets nor rationalisation for his silence.

Pius left no diary or notebook that we know of to explain his thinking. The Vatican archives that might finally answer these questions remain sealed, although a single word from Pope Benedict would open them. So far, the only evidence released has tended to bolster Pius's credentials for beatification. As a group of prominent Christian-Jewish scholars pointed out in a letter to The Times this week, without all the evidence there can be no consensus. The silence of the archives compounds the silence of Pius, and fatally undermines his claim to sainthood.

Looking at those Paris plaques to resistance fighters, I wonder again whether I would have offered a similar reason to remain silent: fear for my family, fear of reprisal, fear of unleashing something worse. Pius argued that it would have been irresponsible to protest openly; you and I might well have made the same excuse. But irresponsibility is a part of true courage.

Pius suffered moral agonies over his decision; he acted for the best, as he saw it, in an excruciatingly difficult situation; he did much to help the Jews, but not enough. All this makes Pius XII fascinating, fallible and important. But it does not make him a saint.

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