Professor Paul A. Underwood of the Harvard-Dumbarton Oaks research library near Washington, D.C., the head of a mission uncovering Byzantine mosaics, has announced that work is nearing completion after almost 20 years of toil.

The wall mosaics were congealed for centuries by plaster and whitewash in two churches--the great Hagai Sophia, and a smaller monastic church, the Karich Djami, both in Istanbul.

The works are considered important because of both artistic and archaeological significance. Underwood, a member of the Faculty of Arts and Sciences, recently returned from Istanbul with a progress report for the sponsoring library, which indicates the cultural value of the works.

Ten Mosaics Uncovered

Ten mosaics in the Hagai Sophia--enough to give a clear idea of the style--have been uncovered. A panel of Christ receiving the supplication of his mother and John the Baptist is included. The works are said to have been fashioned when the church was the center of Eastern Christendom.

The mosaics were made by patterning small Pieces of colored glass or stone into plaster applied to the walls.

Conquering Turks, whose religion forbids such imagery, covered the great mosaics when they converted Hagai Sophia from a church to a mosque.

The restoration process was begun in 1924 by Thomas Whittemore, a Harvard professor who specialized in Byzantine archaeology. Whittemore founded the institute to support the work.