President Reagan said yesterday that it's fine for Chinese canned mushrooms to garnish American pizzas, settling a 2-2 split in the International Trade Commission over whether the imported mushrooms are disrupting the U.S. fungi market.

The president, however, ordered the U.S. trade representative to keep track of future mushroom imports from the People's Republic of China to see if the government should take some action restricting imports in the future.

The American Mushroom Institute complained last June that mushrooms imported from China were disrupting the U.S. market. Pennsylvania mushroom growers, venting their hostility with hyperbole, called it a "Chinese mushroom cloud over the U.S. marketplace."

The Chinese, American importers and Pizza Hut, a major user of Chinese mushrooms, united to fight the American growers' petition to the ITC. The attorney for the importers, Bart Fisher, described the American growers as "motivated by greed and fear."

In a more reasoned statement yesterday, he called the president's decision another sign of the Reagan administration's commitment to free trade and continued commercial relations with the People's Republic of China. He blamed the American industry's lowered sales on the recession, a shift in consumer preference to fresh mushrooms and quality problems.

U.S. Trade Representative William E. Brock said increased imports of canned mushrooms from China have been offset by declining imports from other countries.