This trade dispute has everything: pizza, communists, botulism, tariffs, high-powered Washington lawyers, jobless workers in Pennsylvania, federal regulators, bad jokes and, most of all, mushrooms.

The mushrooms, hordes of them, are coming from the People's Republic of China to the United States, where they wind up decorating the tops of pizza slices. Mushroom growers in Pennsylvania, the self-proclaimed world's mushroom capital, are asking the U.S. International Trade Commission to restrict imports of the canned mushrooms, calling it a "Chinese mushroom cloud over the U.S. marketplace."

The Chinese, the American importers, and Pizza Hut, a major consumer of the imported fungi, have joined forces to fight the Pennsylvania producers. The American canners, in the words of Bart S. Fisher, attorney for the importers, are "motivated by greed and fear," and trying to create a "great wall" of protectionist barriers to the imported competition.

The International Trade Commission is scheduled to hear arguments today on a petition by the American Mushroom Institute for sharp reductions in the amount of canned mushrooms from China that can be imported each year. The institute, which represents the American producers, argues that China, "which is dominated or controlled by communism," is "dumping" its mushrooms, selling them at less than fair market value to capture a larger share of the $400 million-a-year U.S. market.

Fisher, who is known for his unorthodox, high-profile, confrontational approach to international trade disputes, staged a preemptive strike yesterday by calling the press--including reporters from the New China News Agency and Peking People's Daily--to a briefing in the conference room of his firm, Patton, Boggs & Blow.

Across a table laden with fresh, canned and dried mushrooms, Fisher argued that the American canners are victims not of unfair practices by China but of a growing consumer preference for fresh mushrooms, of a recession that has reduced the buying of nonessentials, and of fear of botulism, a lethal form of food poisoning, which Fisher said consumers allegedly associate with the American product.

He said Kennett Square, Pa., the center of the U.S. mushroom industry, is "not the mushroom capital of the world but the botulism capital of the world."

Jack Kooker, executive director of the American Mushroom Institute, said Fisher's charge "doesn't deserve a response. It's a cheap shot, and in fairness to our growers, I don't think we want to subject ourselves to arguing on that level."

He said the American industry "has been impacted" by the imports. "People are being laid off in the canneries. There are a lot of jobs being sacrificed because of these imports." He said he represents "a lot of growers who are third generation. They have a quality product. We are just trying to see that they survive."

The mushroom institute is just one of many U.S. food-producing organizations seeking federal relief from imports, but its petition is unusual because mushroom imports are declining and because the mushroom canners already have special tariff protection as a result of an earlier complaint.

The mushroom industry has undergone a spectacular growth in the past decade, according to figures submitted by both sides in advance of today's hearing, but the market is now dominated by fresh, not canned, products.

Total U.S. production was 58 million pounds in 1971. In 1981, it was 267 million pounds. The fresh mushroom share of the market doubled, from 28 to 56.7 percent of production.

China, which developed a modern, efficient mushroom-canning industry for the European market about a decade ago, was not a factor in the U.S. market until 1980. Then for the first time it was accorded "most favored nation" trade status and was able to challenge Taiwan and South Korea for a share of the U.S. trade.

The result has been rapid Chinese domination of a shrinking market for canned mushrooms. Imports from China totaled 27.4 million pounds last year, nearly double what they were in 1980. But total imports from all countries dropped sharply, from 117.3 million pounds in 1980 to 88.6 million in 1981, after the Carter administration imposed a stiff duty on imports.

Fisher, who represents Nature's Farm Products of Hayward, Calif., a major importer, argued that the Chinese share of the canned mushroom market has been gained not at the expense of the Americans, but at the expense of South Korea and Taiwan, which have been shouldered aside by the cheaper Chinese competition.

The Americans, he said, are trying to "rip off the consumer. They already have tariffs in place. Now they're trying to get quantitative restraints that would cut imports to 5 million pounds a year."

The Chinese, he said, are watching the case with interest, because "trade is a two-way street. We have to import some things from them if we expect to export into that market."