High above the clouds, at 35,000 ft., Adnan Khashoggi’s DC-8 is cruising noiselessly toward his estate in Marbella, Spain. His guests, sipping 1961 Chateau Margaux from crystal goblets with triangular silver bases, lounge on the jet’s cream-colored chamois-and-silk banquettes. His masseur, his valet, his barber and his chiropractor — they accompany him everywhere — are relaxing as well because “A.K.,” as he is known to his employees, is fast asleep on the $200,000 Russian sable spread covering his 10-ft.-wide bed in one of the plane’s three bedrooms. In the plane’s fully equipped kitchen, Khashoggi’s chef is preparing hors d’oeuvres. They will be served on white triangular china, embossed in gold with the letters AK, designed, along with the crystal and flatware, at a cost of $750,000. The plane, which Khashoggi bought in 1982 for $31 million and had reconfigured for an additional $9 million, has the streamlined and futuristic feel of a flying 21st century Las Vegas disco. In the sumptuous lounges, digital panels indicate the time and altitude, and electronic maps chart the jet’s current position. Inside a coffee table, a color monitor shows a view of the ground. Built into the ceiling is an elaborate electronic map of the cosmos, a 50th-birthday gift to Khashoggi, who is fascinated by astronomy. One by one, against a dark background, the outline of the constellations lights up, the tiny stars winking against the blankness. Aquarius . . . Cancer . . . Gemini . . . Then there is Leo, Khashoggi’s birth sign, and as the constellation brightens, a small image of the round-faced, mustachioed Saudi Arabian arms merchant and businessman flashes on and off, on and off. To those who work for him, Adnan Khashoggi is not a constellation but the very center of a mysterious and splendiferous universe. His is a dazzling and ostentatious realm of luxury beyond the dreams of Croesus, a shadowy sphere of deals, arms brokering and billion-dollar investments. But with Khashoggi’s well-publicized role as the middleman in America’s arms-for-hostages deals with Iran, light has been cast on the sometimes shaky financial state of his private and public dealings. Like the arms sales to Iran, several of his recent investments have been ill-conceived, botched deals. The round-figured Khashoggi, who could pass as an amiable neighborhood shopkeeper, has been described as the world’s richest man, though he probably never was and certainly is not now. He sometimes seems to be dancing a curious line between fabulous profits and grim losses. What he was and continues to be is the world’s biggest spender, a man whose unrivaled profligacy gilds his self-image as a grand merchant-statesman. This soft-spoken man with a gift for putting people at ease, the product of a strict Islamic upbringing from one of the world’s most conservative and ascetic nations, has become an international symbol of sybaritic self-indulgence. “I am an artist with my wealth,” he says in quiet measured tones while relaxing in a room at the rear of his jet.