ROME, June 28 (Reuters) - Vatican archaeologists using laser technology have discovered what they believe is the oldest image in existence of St Paul the Apostle, dating from the late 4th century, on the walls of catacomb beneath Rome.

Vatican newspaper Osservatore Romano, revealing the find on Sunday, published a picture of a frescoed image of the face of a man with a pointed black beard on a red background, inside a bright yellow halo. The high forehead is furrowed.

Experts of the Ponitifical Commission for Sacred Archaeology made the discovery on June 19 in the Catacomb of Santa Tecla in Rome and describe it as the "oldest icon in history dedicated to the cult of the Apostle", according to the Vatican newspaper.

The discovery, which involved removing layers of clay and limestone using lasers, was announced a day before Rome observes a religious holiday for the Feasts of St Peter and St Paul.

Peter and Paul are revered by Christians as the greatest early missionaries. Converting on the road to Damascus following a blinding vision of Jesus, Paul took the Gospel to pagan Greeks and Romans and met his martyrdom in Rome in about 65 AD.

Early Christians in Rome buried their dead in catacombs dug into the soft rock under the city and decorated the underground walls with devotional images, often in the Pompeian style.