Egyptian President Anwar Sadat fulfilling a vow he made after his historic visit to Jerusalem exactly two years ago, prayed for peace today in the shadow of the mountain where Moses is said to have received the Ten Commandments 3,500 years ago.

In a ceremony rich in symbolism and laced with paeans to religious harmony, Sadat declared unequivocally that "this place will be open as of now to the followers of the three religions without any limitations or formalities whatsoever."

[Palestinians set off bombs in Jerusalem and attempted a seaborne raid in actions apparently timed to coincide with the second anniversary of Sadat's visit to Israel. Page A13.]

Conspicuously missing from the Mount Sinai ceremony was Israeli Prime Minister Menachem Begin, who was invited by Sadat but who declined, saying he had a heavy schedule. Aides said Begin felt the ceremony should be Sadat's day and that his presence would be inappropriate.

However, attending were Robert Strauss, chairman of President Carter's relection campaign; Alfred Atherton, U.S. ambassador to Egypt; Harold Saunders, assistant secretary for the Middle East, and about two dozen other Amricans invited by Strauss, some of them well-known contributors to the Democratic Party.

Watching was a panoply of religious figures from all corners of the earth, including Moslems, Greek Orthodox, Egyptain Copts, Episcopalians, Cairene Jews, Buddhist monks and Shintoists from Japan, all gathered to celebrate the turnover of the 1,400-year-old St. Catherine's Monastery and the ageless Moses mountain to Egyptain control 13 years after the Israeli Army conquered the Sinai Peninsula during the 1967 Six-Day War.

Sadat had been expected to lay a cornerstone for a $60 million structure planned to include houses of worship of Islam, Judaism and Christianity, but apparently for a lack of time for the necessary fund-raising, that part of the ceremony was postponed.

But color and pageantry were not lacking as more than 600 onlookers gathered in a flag-bedecked parade ground in the ancient valley of Jethro, where the Bible says the children of Israel on their trek from Egypt encamped just before Moses ascended Mount Sinai to listen to God's reproaches from a burning bush and received the stone tablets containing The Law.

According to religious tradition, the spot where Sadat ceremoniously took control of this quadrant of the Sinai Pennisula today is where Aaron told the trembling children of Israel to melt their rings and jewelry into a golden calf and where Moses, outraged by the idolatrous demonstration, smashed the tablets bearing the Ten Commandments.

The scene today was picturesque against a clear blue desert sky, with the craggy brown mountain peaks looking almost like paper cutouts rising starkly from the sandy valley floor.

With a flourish of trumpets echoing off the surrounding cliffs, and a 21-gun salute shattering the tranquillity of the desert, an Egyptian honor guard smartly presented Sadat with his national flag, which the president solemnly raised on a staff in the middle of the parade ground.

As he did, hundreds of Bedouin tribesmen, their camels tethered in the background, cheered wildly, as these durable survivors of countless conquests have done for centuries, including when the Israelis hoisted their flag here 13 years ago.

Two Egyptian soldiers, apparently unaware that they were being watched closely by reporters, moved through the crowd like cheerleaders, urging the Bedouin to raise the tempo of their adulation.

In his speech, Sadat said, "We stand in all reverence on the outskirts of the sacred valley of Tuwa, the holy part of the land of Egypt."

Sadat appealed to the peoples of the world to observe the teachings of God "for the promotion of fraternity and friendship and the elimination of bloodletting, violence and hatred."

"Today, peace has already become a shining reality," Sadat said in allusion to the treaty between Egypt and Israel. He added, "no one can reverse it all."