Mushroom canners from Michigan and Pennsylvania, strongly backed by Sen. John Heinz (R-Pa.), implored the U.S. International Trade Commission yesterday to impose quotas on imported canned mushrooms from China, which they said are destroying the industry in this country.

Imports have declined since stiff tariffs were imposed after a previous commission inquiry, but the canners claim the Chinese have held prices so low that the entire industry is facing heavy losses.

"We're buying mushrooms at 50 percent of what it costs to grow them and we still can't compete," Thomas DiCecco Jr., president of Oxford Corp. of Oxford, Pa., told a commission hearing yesterday. "A lot of our mushrooms are being sold at very depressed prices because there's nothing else to do with them."

"Being a nonmarket economy," China "is not constrained by normal economic considerations like profits, or by the need to have prices reflect true costs," Heinz said in a statement. "In the case of mushrooms, they have essentially 'swallowed' the tariff that has been imposed, maintaining a lower price and driving their competitors out of the market."

He said the result for American mushroomers is that "production is down, earnings are down, and plant after plant is closing. We are threatened with the virtual disappearance of the industry unless we act, and the Trade Act of 1974 clearly gives us the legal basis for doing so."

The American growers and canners have invoked a section of that law providing for import restrictions when imports from a communist country damage a U.S. industry. They are seeking a three-year limit of 5 million pounds a year on canned mushrooms from China. Last year, the United States imported 27.4 million pounds of Chinese mushrooms, most of which are used to garnish pizzas.

China's share of the $400-million-a-year U.S. market nearly doubled from 1980 to 1981, but total imports from all countries dropped sharply, from 117.3 million pounds to 88.6 million pounds.

Because of the drop in imports, no further protection for U.S. growers is justified, say opponents of the proposed quotas, who include importers, China's state food marketing agency, and the Pizza Hut restaurant chain.

They argued that changing consumer tastes, the superior quality of the Chinese product and consumer fear of botulism poisoning after a series of recalls of American mushrooms have enabled the Chinese to capture a growing share of the market.

The International Trade Commission has until Sept. 30 to make a recommendation to the president on the canners' petition for import restrictions.