* Nazis killed 335 in reprisal ordered by Hitler
* Jewish groups applaud German pope's visit
* Last surviving Nazi murderer, 97, under Italy house arrest
By Philip Pullella
ROME, March 27 (Reuters) - German-born Pope Benedict prayed on Sunday at the site where Nazis killed 335 Italian men and boys and denounced one of the worst atrocities of World War Two as "the most horrendous form of evil".
Benedict visited the Ardeatine Caves on Rome's southern outskirts and prayed there together with Rome's chief Rabbi Riccardo di Segni. Seventy-five of the victims were Jews.
In his brief comments at the haunting underground site, Benedict, who was a member of the Hitler Youth when membership was compulsory and later served a German anti-aircraft artillery, called it a "painful memorial of the most horrendous form of evil".
On March 23, 1944, Italian partisans set a bomb on a narrow street, killing 33 German policemen who were part of the occupying powers in Rome.
In retaliation, a furious Hitler approved the murder of 10 Italians for each German killed and ordered that it should be carried out within 24 hours.
The victims of the reprisal, who eventually numbered five more than had been ordered by Hitler, were all shot in the back of the neck in the caves. The Germans later blew up the caves in a vain attempt to try to hide the massacre.
Benedict, speaking at the national monument where many of the victims are buried, said the massacre showed "the abyss that men can be sucked into when, spurred by blind violence, they abandon their own dignity as children of God and their fraternity among themselves".
Jewish groups welcomed the words of condemnation .
"This latest gesture by the German-born Benedict is a further dramatic step in binding the wounds that have disturbed Vatican-Jewish relations in recent years," said Elan Steinberg, vice president of the American Gathering of Holocaust Survivors and their Descendants.
But Steinberg lamented the fact that Ex-Nazi Captain Erich Priebke, who was sentenced to life in prison for his role in the massacre, is currently under house arrest and is allowed to go on shopping trips and other excursions.
"This is a grave offence against man. Those massacred at the Ardeatine caves by Erich Priebke were patriotic sons of Italy. Their memories, and the pope's moving visit, should not be dishonoured and we call on legal authorities to put an end to this perversion of justice," Steinberg said.
Priebke, who was extradited from Argentina in 1994, is now 97.