L. J. DAVIS is a novelist, economist, award-winning business journalist and man of all literary work whose latest book, Onassis: Aristotle and Christina, is being published July 28 by St. Martin's. He describes it as a tale of "inherited wealth and its poisonous effects."

Among the questions Davis raises in the book is whether the $400-million will left by Aristotle Onassis is valid. According to Davis, Greek law requires that a will be handwritten while the maker is sitting uninterruptedly in a single place. "Ari wrote his last will in January 1974, which virtually disinherited his wife Jacqueline, on a flight from Acapulco to New York. Can a plane flying over a multitude of different jurisdictions be regarded as a 'single place'? And we know the plane made a refueling stop in Key West, where Ari paid for the gas with his American Express card. That almost certainly interrupted his writing of the will.

"These questions became important when Jackie threatened to sue over her portion of the will -- all she got was $250,000 a year and some perks. Christina agreed to give Jackie $26 million. It was a shrewd move on Christina's part. One of the things that emerges from the book is that Christina is a crackerjack businesswoman."

Davis had a lot of fun tracking down the characters in the Onassis story. One of the most elusive was Capt. Sergei Danielovitch Kauzov, the Russian who became Christina's third husband and was later divorced by her. The husky, 6-foot-3 Davis donned a sailor's turtleneck sweater and began to prowl shipping offices in London.

"London, of course," says Davis, "is where the Greeks originally set up in the short-haul shipping business. They ran such old tubs -- which often sank under mysterious circumstances -- that Greek names automatically drew an insurance penalty from Lloyd's. Onassis changed that -- he bought terrific new ships and never lost one until near the end of his life. At any rate, I made the rounds of the shipping offices in London and said I was an out-of-work oiler and that I had heard that Capt. Kauzov was looking for one. So someone directed me to him. He ran a Danish-registered cargo ship called the Daniela, which Christina gave him as part of their divorce settlement.

"I didn't get much out of him, but I got an idea of what he was like. My best guess in the book is that his marriage with Christina was cleared at the highest levels of the Politburo. Even today, though he is a Soviet citizen, he is allowed to live openly in London."

Before donning his reportorial turtleneck on the trail of the Onassis story, Davis had written five other books, including four novels: Whence All But He Had Fled (1967) Cowboys Don't Cry (1968), A Meaningful Life (1971) and Walking Small (1974). They all concern the vicissitudes of city life, particularly focusing on ironic accounts of middle-class people rehabilitating residences in slum neighborhoods. Despite critical praise, they sold in miniscule amounts in America, but did much better in Britain, where Davis is seen by some as a kind of Evelyn Waugh of the American urban crisis.

"My British editor, Miles Huddleston at Constable in London, tells me that I am regarded as one of the premier American comic novelists," says Davis. "One night I got a call from a friend at the British Broadcasting Corporation. He told me he had visited a remote but sort of modernized village in Kenya and that the library there had all my novels. He said the librarian described me as 'the famous and well-known author, L.J. Davis.' Ha!"

Perhaps disappointed by sales of his novels, Davis turned to journalism in the late '70s, and is currently a contributing editor for Harper's and Manhattan Inc., specializing mainly in business and economic topics. In 1983, St. Martin's issued Bad Money, a book that according to Davis, predicted "to the month, the week, the day" the emergence of shaky Third World loans as a topic of serious concern. He is currently working on a book on the Securities and Exchange Commission, stock scams and corporate raids, which will probably be out in 1988. California Dreaming CALIFORNIA, it hardly needs saying, is a land of many faces, and its publishing business is too. I recently talked to publishers of two small presses who see the world in very different ways. Noel Young of the Capra Press in Santa Barbara is making a stir in the small-press world with an innovative way of publishing works of fiction that are too short to be books on their own yet are too long for literary magazines. Young's innovation is Capra Back-to-Backs. Here's how they work. On one cover is a work by a well-established serious writer, let's say Confessions of a Barbarian by Edward Abbey, weighing in at 87 pages. Flip the book over and turn it upside down, and there on the cover is another work by a good but lesser-known writer, Red Knife Valley by Jack Curtis, 94 pages long.

Separately, the books would probably not be publishable. Together, they make a nice package of 180-plus pages. The Abbey-Curtis volume is the seventh to be published by Capra Press since it began the Back-to-Backs 2 1/2 years ago. The books are bound in a manner more reminiscent of France than America -- with a flap softcover and acid-free paper with a rough fore-edge. They sell for $7.95 a volume.

The other California publisher is Scott Alexander of the Rhino Press Inc. of Laguna Hills, which is devoted exclusively to selling the works of Scott Alexander. Let Scott tell how he got into publishing:

"It was six years ago. I was 23. I'd just lost all my money in a mobile car-wash business. I was married, getting deeper and deeper into debt. But I didn't want to work for anyone else. I knew it was up to me. I sat down and wrote my philosophy -- that in the business world you had to be like a rhinoceros. You had to have a thick skin. You had to have that hot muggy rhino breath. Above all, you had to charge through the jungle. The opposite of a rhino is a cow. Cows are people who hate their jobs, but don't do anything about it. They just sit around and whine and complain.

"When I finished the book, I thought it was worth publishing. So I called it Rhinoceros Success, printed up a thousand copies and started selling it myself. After a year and a half, I'd only sold 2,000 copies, but I kept charging. Finally in 1982, things turned around and I sold 200,000 copies. In 1983, I wrote a sequel called Advanced Rhinocerology and in 1984 I did Rhinocerotic Relativity. Those make up The Rhino Trilogy."

The books of The Rhino Trilogy have sold a total of 500,000 copies, but Rhinoceros Success accounts for four-fifths of that number. Scott Alexander doesn't think too highly of bookstores. Most of his sales have been bulk purchases by groups where motivation of sales people is an important factor, such as Amway, Mary Kay Cosmetics and Tupperware. "And I've sold hundreds of copies to the United States Marines to use with their recruiters," says Alexander.

Along with his books, Alexander has come up with a catalogue full of rhinoceros-related items, including a wooden fork-and-spoon salad set with carved rhinos on the handles and his most expensive item, an $800 rhino head made of papier-ma che'.

Alexander recently took a booth at the American Booksellers convention in New Orleans to promote The Rhino Trilogy and came away with plans for other publishing projects. "Cookbooks are very hot," Alexander says, so he is planning A Rhino Cookbook. "We've got a mailing list of people all around the country who buy our rhino products and I'm asking them all to send in a recipe." And he wants to extend the rhino concept to a children's book. "It won't be about the business jungle," he says, "but we'll adapt the rhino concept to schools. It'll say, 'C'mon little guys, put on your thick skins, and get out there and make it happen. Don't be a little cow -- keep charging.' " In the Margin TIME-LIFE BOOKS of Alexandria last month celebrated 25 years in business and its 10th year in the Washington area. The world's largest publisher of direct mail books, it has sold over half-a-billion books worldwide . . . In the fall, Knopf will publish the memoirs of Yelena Bonner, wife of Soviet dissident Andrei Sakharov. The book will also be published simultaneously in seven other countries: Britain, France, Germany, Italy, Denmark, Norway and Sweden . . . Little, Brown has signed Janet Dailey to a two-book contract. The first book, Daughters of the Wind, will be published in September. Dailey is the top-selling female author in America with 113 million copies of 82 books in print. She has been translated into 19 languages . . . Those with an interest in colonial history will be saddened to hear of the death of Prof. Stephen Botein of Michigan State University. An expert on the legal profession and the book trade in the colonies, Prof. Botein died last month of a cerebral aneurism. He was 44. He had spent the last year as guest editor at the Institute of Early American History and Culture in Williamsburg.