ROME, March 20 (Reuters) - Pope Benedict washed and dried the feet of 12 men at a traditional Holy Thursday service commemorating Christ's gesture of humility to his apostles on the night before he died.

The 80-year-old German-born Pope, approaching the third Easter of his pontificate, called on Catholics to be of service to each other and to confess their sins.

"We need the foot washing, the washing of our sins every day. And for this reason we need to confess our sins," the Pope said.

During the service, he poured water over the right feet of 12 men sitting on raised platforms, and dried them. The ritual was held in Rome's Basilica of St. John's in Lateran, the Pope's cathedral in his capacity as bishop of the Italian capital.

Earlier on Thursday, the Pope said in a ceremony at St. Peter's Basilica that priests should be vigilant for evil and stand firm on Church truth despite "the currents of time".

Both services were to mark Christ's founding of the priesthood at the Last Supper on the night before he died.

On Good Friday, the Pope will hold two services commemorating Christ's crucifixion, including a Via Crucis (Way of the Cross) procession around the ruins of Rome's Colosseum.

He says an Easter Eve mass on Saturday night and on Sunday will deliver an "Urbi et Orbi" (to the city and the world) blessing and message.

The Pope's heavy Easter schedule comes in the wake of a threatening message by Al Qaeda leader Osama bin Laden, who said the publication of cartoons mocking Islam's Prophet Mohammad was part of a "new crusade" involving the Pontiff.

The Vatican rejected the accusations as "unfounded", and noted the Pope had been quick to condemn the cartoons. (Writing by Phil Stewart)