Americans are eating record numbers of mushrooms and the fresh and canned prices for the fungi, which - like humans - take in oxygen and give off carbon dioxide, have been rising steadily.

This, one might think, would make for an altogether happy U.S. mushroom industry.

U.S. mushroom canners, however, like U.S. shoe and television manufacturers, are threatened by imports from Asia and have been seeking federal government protection from the lower-priced Taiwan and South Korean canned buttons, steams and pieces.

Their wounds smart all the more because they believe it was the U.S. government - through its foreign aid programs - that got Taiwan and South Korea started as mushroom growers and canners.

The agency for International Development never thought wher e the Asian mushrooms would be sold, complain the U.S. canners, who have seen their share of the U.S. market slip from more than 80 per cent to 55 per cent in 15 years. In the year ended June 30, 1976, the import share of the market came to $46.2 million.

A spokesman for AID said no official could be located who was involved in helping Taiwan or South Korea get started in mushroom production. He pointed out that it all began well over 15 years ago in Taiwan.

The Mushroom Processors Tariff Committee, which is rooted within the Washington law offices of Pope Ballard & loos, told the International Trade Commission that imports must be restrained to enable the U.S. processors to regain "at least 75 per cent of the U.S. market."

All sides agree that canned agaricus bisporus (an adaptation of the common field mushroom and the only type cultivated for processing) taste the same whether they are stuffed into brine-filled glass jars here, in Taiwan or in South Korea.

But labor costs and the rising price of fresh mushrooms have made it impossible for the U.S. industry to maintain its market share.

Stems and pieces can be canned by fairly automated procedure, a government expert said, but the buttons caps) are best handled by people, the tremendous wage differences [WORD ILLEGIBLE] been the United States and the [WORD ILLEGIBLE] producers is no longer compen- [WORD ILLEGIBLE] for by greater yields here. [WORD ILLEGIBLE] average price of a case of 24 4- [WORD ILLEGIBLE] in the third quarter of 1976 was $9.44 for American stems and pieces, compared with $8.47 for Taiwanese and $8.30 for Korean equivalents. A case of buttons the same size was $11.32 if American, $10.04 if Taiwanese and $9.89 if Korean, according to ITC figures.

In additions, as Americans' consumtion of fresh mushrooms has increased, the price has soared, leaving the Asian producers with the second advantage of a cheaper mushroom to process.

Twice, the International Trade Commission has found under Section 201 of the 1974 Trade Act that serious injury has been done to U.S. mushroom processors.

Last year President Ford denied the industry any relief, and President Carter followed suit March 10.

Instead, the President's office of the special trade representative has attempted several times to arrive at informal understandings with the South Korean and the Taiwanese on how many mushrooms they will ship.

But there is no specific agreement, and the President directed the ITC to compile quarterly reports on mushrooms to detect any abrupt changes in imports or consumption.

U.S. canners are particularly resentful and government officials particularly skeptical because last summer after Ford turned down the first ITC recommendation of relief, "Taiwan cleaned out its mushroom caves and shipped everything it had," one expert said.

"Korea appreciated that it doesn't look right for imports to soar" just after the U.S. industry is denied relief, he added. Still, during the summer months, total imports reached ghe level of total U.S. consumption.

Carter's decision on mushrooms was his first on a question of providing import relief to a U.S. industry.

It was based largely on the potential inflationary impact of any action, since fresh mushrooms had become greatly more expensive over the last 18 months.

In addition, the relief recommended by the ITC is intended to provide an industry time to adjust to new circumstances and become competitive. "It was not clear the U.S. industry could have done this," one official said.

Over the years, some mushroom processors have been going out of business, he added, but others have entered the field. "It didn't look like the industry was really falling apart."