A book charging that a "beef mafia" is rigging prices and controlling markets has set off such a furor here that the author plans to leave the country to seek a new job and safety.

The book titled "Why Is Beef So Expensive?." has sold 10,000 copies in this country where beef prices go as high as $50 a pound. It charges that the beef industry rakes off exorbitant profits while the government limits beef imports from America and Australia.

Charges in the book, which received favorable reviews, have been bitterly denied by government and industry spokesmen as "rootless rumor."

Some alarming things have happened to author Tetsuji Yokota, 36, since his book was published. Fired from his job with a meat trade journal, he says an industry blacklist is keeping him out of work. Furious industry insiders grabbed and threatened him, and he fears further trouble.

Glancing about nervously during an interview in a Tokyo hotel lobby this week, he said he felt endangered and was preparing to leave the country.

On the positive side, whether by coincidence or not, the price of beef is expected to go down 20 per cent soon by government order. With constant newspaper stories and television interviews. Yokota is fast becoming a housewives' hero -- a courageous Robin Hood challenging the powerful beef barons. In Kobe, a meat store owner is running for Parliament on a cheaper-beef ticket, and calling for a boycott until prices drop.

The Japanese taste for beef is small --America's red-blooded average consumption of 123 pounds. It is expected to increase steadily, however, as fish, the nation's principal protein source, gets more expensive.

Beef is incredibly expensive because the Japanese government, determined to retain partial self-sufficiency in food supplies, props up a grossly inefficient and uneconomic domestic beef-raising industry. Foreign meat-importers who could put the Japanese farmers out of business in less time than it takes to grow a decent sirloin are hindered by quotas and a blatantly protectionist array of duties and special surcharges that Yokota claims increase the price of imported beef 10 times.

The Japanese lack farmland, fodder and grain to produce beef economically by world standards. An American embassy agricultural expert, Philip C. Holloway, calls the Japanese explanation of wishing to retain food self-sufficiency "a ridiculous argument."

Japan imports 8 million tons of feed grain from the United States each year to feed cattle and other livestock, "so they can't ever be truly selfsufficient," Holloway explained.

In 1976 the Japanese produced 300,000 tons of beef and imported another 135,000. By 1985, the government hopes, increased domestic production will leave only 20 per cent of their market to imported meat.

"Our aim is a stable food supply," said Ministry of Agriculture official Shigeru Motai. "The international meat trade is too dangerous for us to have a 50 per cent reliance on imports."

The extraordinary economics of beef were revealed in January when a Japan Airlines cargo jet freighter crased on takeoff from Achorage, Alaska. Killed with the crew of five were 56 American cattle -- not high-priced breeding stock, but beef on the hoof air-freighted to beat the quota system and still competitive in price with hand-raised Japanese beef.

The principal target of Yokota's investigation was the quasi-governmental Livestock Industry Promotion Corp. In theory, the corporation protects producers and consumers by keeping beef prices within a stable price range.

From his intimat knowledge of the meat industry's murky workings, Yokota says the corporation actually performs a different function. He accuses it of price-rigging to drive down the price Japanese trading companies pay for American and Australian cattle and to force up prices at butcher shops.

Standing between the American beef lots and the Japanese sukiyaki restaurants is a Byzantine distribution system in which assorted food-processors, brokers and monopolistic retail associations reap tremendous profits by jockeying the imported beef from one to another.

Yokota asserts that the public is being rooked by a conspiracy involving the retired Agriculture Ministry officials who run the livestock corporation, conservative politicians, and powerful figures who have cornered the meat distribution system. Rummaging through a bag of papers, the writer whispers the names of politicians he believes are paid off to preserve the present cozy relationship. The payoffs are substantiated by industry sources, Yokota says.

The ruling Liberal Democratic Party depends heavily on the farm vote and thus has a vested interest in protecting cattle-raisers from low-priced foreign meat, he argues, and manipulates the market through the corporation.

Yokota admits that he has no evidence to prove financial wrongdoing by the corporation. Kashio Hiramatsu, the organization's vice-president, commented: "He is talking nonsense. All this talk of dirty connections and money to politicians -- but there is never concrete evidence of where and when and to whom this money is supposed to have gone."

Hiramatsu said the livestock corporation's books are checked by government auditors.

"Corruption is impossible." he added.

Both sides fear that the beef storm will damage Japan's international reputation. New Zealand has already threatened to exclude Japanese fishing vessels from its 200-mile zone unless Tokyo agrees to take more beef.

Regardless of whether the sensational charges of massive multimillion-dollar corruption are verified, the Japanese government is unquestionably employing protectionist policies of the kind it opposes in other nations.

A superior American grain-fed steak imported for $2.50 goes on sale here at a minimum of $13.50. In splitting up the slim import quota, the Japanese favor Australia, a chief supplier of raw materials with an 88 per cent share. American beef suppliers, unless they want to join the on-the-hoof airlift, get only 12 per cent.