ROME (Reuters) - Pope Francis had to be helped up the steps to an altar at a Rome basilica on Monday after stumbling in public for the second time in three days.

Two church officials flanked the 78-year-old pontiff and took him by the arm as he faltered on his way up the steps during a service in the Basilica of St. John Lateran.

On Saturday, the pope tripped on the steps of St. Peter's Basilica, stopping his fall with his outstretched hands, before two aides helped him back to his feet.

Last month, the Vatican dismissed an Italian newspaper report that the pope was suffering from a benign brain tumor, saying the pontiff was in good health.

The pope lost part of one lung to disease as a young man and is known to suffer some leg pain due to sciatica, for which he undergoes regular therapy and which might explain his apparent trouble climbing steps.

In September, the pope slipped as he was climbing a staircase to board a flight during a trip in the United States. He quickly got back to his feet, without any assistance, and entered the plane without any further difficulty.

Francis has said he expects his papacy to be short, and ends every weekly Angelus address with an exhortation to the world's 1.2 billion Catholics to pray for him.

(Reporting by Isla Binnie; Editing by Crispian Balmer and Richard Balmforth)