The U.S. International Trade Commission yesterday ordered a new investigation into the nine-year-old finding that Japanese television sets were being dumped in U.S. markets, possibly overturning one of the government's largest import controversies ever.

The Commission, at the request of Sanyo Electric Co. Ltd and three other Japanese television makers and their American subsidiaries, said it would reopen the investigation to determine whether the importing of Japanese television sets now threaten to materially injure the domestic market. The Japanese manufacturers said circumstances have changed since the dumping finding nine years ago.

In 1971 the commission said that the imports were injuring American television manufacturers. The Commerce Department then found that the importers were dumping, that is selling goods here at prices below their costs of production, and thereby injuring or threatening to injure the domestic market.

That decision led to a nine-year disagreement between the importers and the U.S. government over how much the importers should pay in dumping duties. The major importers finally agreed last April to pay up to $77 million to the government in outstanding dumping and civil fraud claims.

The 110 importers of the sets agreed to settlements of claims on $2 billion worth of television sets imported here between 1971 and April 1, 1979.

The Japanese manufacturers claimed in their petitions to the commission that since the 1971 finding, circumstances have been changed and that Japanese television imports no longer pose a threat to American manufacturers. The Japanese claimed that imports have declined substantiall since 1971, from 3.7 million units to 1.1 million last year, according to an ITC official.

The Japanese also said that many of the Japanese firms have production facilities in this country, therefore few television sets will be imported.

Last year 16 million domestic and imported television sets worth $3.5 billion were bought in America, the ITC said.