As U.S. Ambassador to Israel, Samuel Lewis holds one of the State Department's toughest jobs. Even in quiet times Lewis, 51, puts in 15 hours a day six or seven days a week. Last month relations between Washington and Jerusalem became particularly strained by Israel's annexation of the Golan Heights from Syria. After U.S. officials rebuked Israel, Lewis was forced to sit silently for 45 minutes while Prime Minister Menachem Begin tongue-lashed him. "You have no moral right to preach to us," Begin thundered. "Are we a banana republic?" Last week the Ambassador was recalled to Washington, along with the U.S. envoy to Cairo, ostensibly to brief Secretary of State Haig on his upcoming Mideast trip. "I've had a particularly difficult time in the past two weeks," Lewis cheerfully admitted. "I wish I had been diving instead."

Lewis has long been admired for his remarkable equanimity—and its unlikely source: the relaxation he finds in scuba diving in the Red Sea. "Two weeks after I arrived in 1977, during those hectic days of the peace process, I realized the psychic tensions of this job were going to be enormous and I would need some escape from politics," Lewis recalls. "The moment I got to Sinai, I fell in love with the place—the contrast between the stark, dry, barren cliffs and the deep blue of the Gulf of Aqaba." A longtime snorkeler, Lewis had never had the chance to dive with an air tank until he moved to Tel Aviv. He began taking lessons in the embassy pool. By August 1977 he was certified—and addicted. "The underwater life in the Red Sea is incredible," Lewis says. "The Caribbean is beautiful, but the Red Sea is better, the water even clearer. The fish are so much more prolific, the colors much richer. And what a variety of coral!"

On a recent diving expedition near Dahab, Lewis persuaded two friends to explore an underwater arch. "Let's go into the blue hole," he suggested. "You go down 55 meters [about 180 feet] and see magnificent black coral trees in very dark blue water. As streaming in from the open sea." "Look, Sam," said Pete Peterson, his naval attaché and an ex-frogman, "this is much too deep for us. Fifty-five meters is for pros, not sports divers. We don't have the right equipment."

"No problem," the Ambassador retorted. "I've done it twice before." Indeed, the dive had its perils. Lewis almost ran out of air on the way and had to borrow from a companion's mouthpiece. "I'm just not in too good condition, so I breathe more than someone who's really in shape," the 185-pound, 5'11" Ambassador explains. "But I knew the others still had plenty of air. I had calculated it." Lewis is enough at home under the sea to make sport of its dangers. He has photographed sharks from 25 feet and even played with fierce moray eels.

Lewis' dives have taken him in search of sunken treasure too. In the indoor garden of his residence outside Tel Aviv, alongside a 17th-century B.C. jug given him by the late Moshe Dayan, Lewis keeps a soup plate from the Farouk, an Egyptian ship torpedoed by the Israelis during the 1948 War of Independence. "Lots of Egyptian soldiers died," Lewis says. "It is like an underwater war cemetery. We got directions from an Arab fisherman off the Gaza coast. We found guns, dishes, helmets and navigational equipment." Another prize the Ambassador recovered was a cup and saucer from the galley of the Dunraven, a mystery ship when Lewis dove to it in 1978. "We swam inside the entire length of this spectacular wreck," he recalls. "It was lying upside down festooned with beautifully colored coral. Groupers—up to 200-pounders—lived there, and there were green and blue clouds of smaller fish." At first no one knew the ship's origin. For a while Lewis thought it might have been used by Lawrence of Arabia to carry gold, but a BBC research team eventually determined it was an ill-fated British merchant vessel (she had 10 captains in three years) that foundered in 1876. During one of his dives Lewis was separated from his companion. His light failed, his air supply dwindled, and for a few minutes he lost his way. "It was the scariest moment I've ever had underwater," he admits.

Israel is Lewis' first ambassadorship after a distinguished career in the foreign service. Born in Houston, the son of an engineer, he majored in international relations and history at Yale and got his M.A. at Johns Hopkins. Previously he has served in Italy, Brazil and Afghanistan, on the National Security Council, and as Assistant Secretary of State for United Nations Affairs.

Besides his diving, Lewis plays tennis—"I'm an enthusiastic mediocre club player"—savors rare moments with history books and Ken Follett novels, and seldom misses the Israel Philharmonic. He and his wife, Sallie, have a daughter, Grace, 24, who is an aspiring artist working as a truck driver in Boston, and a son, Richard, 19, at James Madison University in Harrisonburg, Va. Sallie's mother has lived with the Lewises since she was widowed.

Israel is scheduled to return the Sinai to the Egyptians in April, and when that happens Lewis hopes to start a new kind of shuttle diplomacy. "I have every expectation that I will continue to dive there," he says. He hopes it will also continue to provide some respite from his high-pressure job. Prime Minister Begin may have other ideas. In the past he has interrupted Lewis' diving trips so often with calls that he once half-jokingly warned the Ambassador, "Perhaps I'll lay an underwater phone cable to you."