ST. CATHERINE'S MONASTERY at the base of Mount Moses in the Mount Sinai massif now is accessible from Egypt as well as from Israel, following the recent return of Sinai territory to Egypt under the peace accords.

The 14-centuries-old monastery is a storehouse of historic and religious treasures. It owns the world's greatest collection of icons and its possession of ancient Christian manuscripts is said to be second only to that of the Vatican.

Although somewhat difficult to reach, the holy citadel remains one of the most remarkable sites -- not only in the Sinai Desert, or in the Middle East for that matter, but anywhere in the world. Half-fortress, half-villa, with walls 15 feet high, it resembles a square with walls running about 90 yards on each side. It nestles, oasis-like at 5,012 feet, about 2,500 feet below the summit where most Biblical scholars believe Moses received the Ten Commandments. The summit is snow-capped in winter.

The monastery, known locally as Santa Katerina, provides for pilgrims limited and very modest accomodations. But such a stay offers a unique opportunity. The vistor will awake at 3 a.m. to a clanging bell that beckons him to undertake a scrambling climb to the summit via one of two paths, and witness the type of spectacular sunrise that only a desert atmosphere can provide. A venturesome, sleepingbag traveler may do likewise.

It can be an exhilarating experience, on this spot which is so meaningful to the three great monotheistic religions, Judaism, Christianity and Islam, which regard Moses as one of the prophets. One becomes aware of an awesome quiet and a terrifying beauty. The spectatator may envision scenes from the Exodus, for the terrain has changed but little since Moses led his people out of the land of the Pharoahs. Imagination can conjure up the children of Israel on their long search for the Promised Land, the famed clay tablets, and perhaps even the Burning Bush from which the Lord spoke to Moses.

In the courtyard, far below, a thorn bush does bloom adjacent to the Chapel of the Burning Bush. Skeptics claim it is not even an offshot of the Biblical bush, but it is nevertheless a reminder of the Bibical incident. Standing about eight feet high, the bush blooms in season with an orange-yellow blossom. Some observers say that in a certain sunlight the bush appears to blaze as if one fire.

The site of the monastery had been a magnet for pilgrims since the early days of Christianity. Hermits and monks built shelters there but they were subjected to dangers and faced many problems. In 527 A.D., the Roman emperor Justinian ordered a walled complex constructed to protect a group of monks from harrassment by desert nomads. Justinian was enraged when he learned that his architect had built the compound out in the open rather than on a more strategic mountain top. The architect paid with his head. Actually, the architect was wise for the site had a plentiful supply of water and thus cultivable land.

On Nov. 14, Archbishop Damyamos of the Greek Orthodox Church held a rare press conference in a room adjacent to the library with its repository of countless rare manuscripts and priceless pieces by Byzantine art. The bearded patriarch met the newsmen in a room adorned with portraits of church dignitaries dating back through the centuries. Two other monks watched silently as the archbishop answered questions in English, one of a number of languages at his command.

The church leader said the monks are longing for a return to the contemplative quiet of the desert. But he is not inhospitable to all visitors, he said, making a distinction in the term. "Pilgrims are welcome," he said, "but sightseeing tourists create problems."

The interview took place the day before the military transfer of the area by the Israelis to the Egyptians. Egypt has since indicated there will be new rules regarding travel to the monastery, with access via Egypt from Israel and other foregin countries. Tourists will not use Egyptian travel facilities.

Prior to the 1967 War, the monastery has been almost as inaccessible as a lamasery in Tibet. When Israel captured the Sinai, a military airport was built about 20 miles from St. Catherine's. In succeeding years thousands of Tourists, mostly Israeli but including Americans and other nationalities, have flocked to the site to view the historic treasures. An asphalt road extends about five miles from the small airport toward the walled compound but it ends abruptly, a concession to the monks. From that point the road is a torturous sandy path best suited to heavy-duty vehicles and trucks.

The archbishop expressed concern about a plan which President Anwar Sadat of Egypt suggested some months ago. Sadat proposed a 'triple shrine' to commenmorate the new peace accords and asked that it be built at or on Mount Sinai. The archbishop made it clear he would like to see the proposed edifice (church, synagogue, mosque) built a long distance from St. Catherine's. He fears the area would become a tourist mecca.

"We don't yet know the details of any such plan," said the Greek prelate. "We will have to discuss our position with Egyptians." And even if such a structure should materializee, he feels that each denomination should have its own section. In short, the archbishop does not envision St. Catherine's becoming an ecumenical house of worship.

Five days later, Sadat formally took back the Mount Sinai territory and an Egyptian flag was hoisted over a nearby encampment. He declared the area open to all -- Jews, Moslems and Christians. He then motored to the monastery where the monks laid out a carpet of pink desert flowers and olive branches.

Referring to his previous proposal for a single house of prayer, Sadat said "it doesn't matter what it looks like." He said there should be some sort of monument to the Israeli-Egyptian peace effort. "The meaning of it is important," he said. "Even if it is only a small plaque." Sadat spoke on the second anniversity of his historic trip to Jerusalem, which resulted in the Camp David peace accords.

Actually there is a small mosque inside the walled compound. The white building symbolizes the strange relationship between the monastery and the surrounding desert. No one seems precisely sure why it was built but the legends about it are varied and charming.

There is anothr small mosque near the peak of Mount Moses where the morning climber may rest. Local tribesmen ascend the mountain to pray there at appropirate times in the Moslem religious year. Nearby is a small chapel, and a 500-year-old cypress tree standing in splendid solitary isolation.

The centerpiece of the monastery is the Church of the Transfiguration, containing nine chapels are decorated with priceless icons. In front of the altar are two golden caskets, containing St. Cahterine's head and a part of her arm. St. Catherine was tortured for her religious beliefs and later beheaded in the 4th century.

Outside the walls is a building called the Charnel House. In this former chapel sits the skeleton of St. Stephen, who built a small confessional on the mountain side for ascending pilgrims. He died in 580 A.D. The skeleton sits upright clad in a purple robe which was a gift from tsarist Russia. The monks say the dry, hot climate keeps the remains and the vestments in a good state of preservation. Near St. Stephen are the skulls and bones of the monks who have died in the monastery. The bones are exhumed from a nearby cemetery after a suitable period of time.

The sight may not be very cheering, and some might find it gruesome. But somehow, in that setting, it does not seem objectionable. The entire vista, the elemental force and milieu of the desert, contribute to the psychological effect and seem to underscore the Bibical reminder: "For dust thou art, and unto dust shalt thou return."

One can only speculate on how the monks regard the transfer of sovereignty over the territory. The centuries have seen many occupiers come, stay awhile and then leave. These have included the Romans, the arabs, the Turks and the Crusaders. Even Napoleon held jurisdiction over the monastery for a few short years at the close of the 18th century. No doubt the monks are mindful of the interruption and distraction from their desired contemplative quiet. But is is probable that they view it philosophically, the fanfare and the flag raising as just another historic happening.