As a Moslem, Adnan Khashoggi could have had many wives. But he only took one - and if she has her way in court, it will literally cost him a fortune.

Last week, while the legendary Saudi Arabian financier was sailing on one of his yachts in the Mediterranean, his wife, Soraya, filed papers in Los Angeles Superior Court seeking a legal separation and a property settlement of $2 billion and change ( $540 million). That is half the fortune she estimates her husband has earned as the Mideast's main middleman, whose conspicuous international life-style reportedly was the basis for Harold Robbins' novel, "The Pirate."

With the sums involved, it is not surprising that Soraya Khashoggi's attorney is Marvin Mitchelson, the flamboyant Los Angeles divorce lawyer whose clients have included Bianca Jagger, Sara Dylan and Michelle Marvin - in her landmark property settlement suit against actor Lee Marvin. Midway through that trial, Soraya Khashoggi, 34, asked her English attorney to look up Mr. Mitchelson," Mitchelson says. She subsequently moved to Westwood, only a few miles away from Mitchelson's office in futuristic Century City. At the time, Mitchelson predicted that after the Marvin suit, he would handle "the biggest one of all time." True or not, it is hard to imagine a fortune larger than that of Adnan Khashoggi.

Operating as a high-powered intermediary between Western corporations and the Saudi Arabian royal family since he dropped out of Stanford University in the mid-1950s 43-year-old Khashoggi has amassed what is believed to be one of the largest personal fortunes in the world.

In an interview last Thursda-, Mitchelson said that among Khashoggi's assets are nine homes throughout the world, three jets (two 727s and a DC9) based in Los Angeles, 97 percent ownership of California's Security Banccorp (15 branches) and real estate and other holdings in the United States totaling $200 million to $300 million.

In a June 1977 Fortune magazine article, Khashoggi boasted that in the previous six years he had earned commissions of $575 million by arranging and expediting sales to Saudi Arabia totaling $11.5 billion. He reportedly has had a hand in 80 percent of all arms sales in Saudi Arabia from the United States and other countries. A single sale of French tanks ( $600 million worth) brought him a $45 million commission, according to Fortune, which fixed his net worth in 1977 at more than $500 million.

Known as "A. K." to his associates, Khashoggi gained access to the Saudi Arabian elite through his father Mohamed Khashoggi, who was personal physician to the late King Ibn Saud.He attended Victoria College in Alexandria, Egypt, an elite British boarding school whose alumni include King Hussein of Jordan. Later, Khashoggi spent a year at Chico State University near San Francisco and a single semester at Stanford University. While at Stanford, he lived in a four-bedroom Palo Alto home with a pool, a Japanese butler and a secretary who also helped with his homework.

He left Stanford when the curriculum began interfering with his wheeling and dealing. Shortly thereafter, while still in his early 20s, he put together his first big-ticket sale: a batch of Kenworth trucks sold to the Saudi royal family. That transaction earned him a commission of $245,000.

Soraya Khashoggi was Sandra Jarvis-Daly of Leicester, England, when she met Khashoggi, apparently while visiting Paris with her mother. She was 15, "or so she tells me," Mitchelson said, when the couple married in 1962 in Moslem ceremonies performed in both Saudi Arabia and Lebanon. The couple honeymooned in Las Vegas.

After 13 years of marriage and five children, Soraya Khashoggi's suit claims that her husband illegally and secretly divorced her in 1974 through a proxy acting with Khashoggi's power of attorney in the Beirut Islamic court.

Michelson claims that Khashoggi has accumulated wealth far in excess of $4 billion through the couple's joint efforts. "She comforted, aided and assisted in his business affairs," Mitchelson says. The suit claims that she assisted in delivering a "gift of expensive jewelry" to Julie Nixon Eisenhower during her father's presidency. (In a past Penthouse magazine article, Khashoggi was quoted as saying, "I met Nixon in Paris in 1967 and we had dinner at the Rasputin New York he gave a cocktail party for me.")

A spokesman for Khashoggi's Beverly Hills law firm - Ball, Hunt, Hart, Brown and Baerwitz - declined to comment on the specifics of the suit. Khashoggi will challenge the California court's jurisdiction, the spokesman said: "We hope to make it short and sweet."

Soraya Khashoggi claims in her civil action (which Mitchelson filed apart from the legal separation action) that among other business services she performed for her husband (such as reading contracts written in English), she: "engaged in banking transactions in Switzerland and elsewhere for top executives of defendant Khashoggi's American principals"; "delivered gifts of cash to one of the princes of Saudi Arabia and to the parties' American principals and their wives and ladies"; and participated in "negotiations with representatives of American corporations."

In addition to the $2-billion property split, Soraya Khashoggi is asking for $500 million in punitive damages and $40 million in general damages (figured at $1 million a year for the next 40 years), claiming that her husband reneged on a contract that the couple entered into orally in Cannes, France, in 1974.

At the meeting, Soraya Khashoggi says her husband told her that he planned to divorce her, but promised to support her "for the rest of her life" in the manner to which he "had caused her to become accustomed." In return, she says that she promised to raise their children as Moslems and refrain from hiring an attorney to represent her in the impending divorce or from making any claim to any of the wealth accumulated during the marriage.

Soraya Khashoggi's suit claims that if she violated any part of her promise, her husband threatened to prevent her from ever seeing her children again, disinherit the children, cancel her Saudi passport and declare "her blood to be legal," by which she took him to mean "that under Islamic law it would be lawful for her to be put to death without judicial process."

The couple was reconciled "several times" since the Cannes meeting, Mitchelson said. But he claimed that in June of this year Khashoggi repudiated his side of the agreement.

Just as Michelle Marvin's suit sparked thousands of similar cases brought by unmarrieds against their partners, Mitchelson hopes the Khashoggi affair will "encourage Moslem women to come out from behind their veils and demand their rights.

"Whether it be a Saudi Arabian businessman or a rock star like Mick Jagger [whose wife, Bianca, Mitchelson represents in a $12.5 million divorce action], these guys operate internationally, they're all over the place, there isn't any place where they have their abode," Mitchelson said.

"Why shouldn't their wives have the same client's half in this case staggers the imagination, why should she have any less than the law entitles her to?"

Mitchelson said that because Khashoggi "claims he lives out of his airplane as much as any place else," the attorney served legal papers on his airplane in Los Angeles.

"Keep in mind that the Koran talks about fair and just treatment of the wife," Mitchelson said, chuckling. "Of course we have a copy. I'm studying it very carefully. This is new territory." CAPTION: Picture 1, Soraya Khashoggi, by UPI; Picture 2, Soraya Khashoggi and lawyer Marvin Mitchelson, by UPI