The Commerce Department said yesterday it had begun an investigation into whether steel from eight countries was being sold in the United States at less than fair value.

The countries involved are Austria, Czechoslovakia, East Germany, Hungary, Poland, Romania, Sweden and Venezuela. Through last September, those nations had shipped $217 million worth of steel products to the United States in 1984.

The investigation is being launched in response to a petition filed by U.S. Steel Corp. on Dec. 19, contending that the foreign steel makers were selling their goods in this country at prices below the cost of production.

If the government finds this to be the case, it could impose tariffs to raise the price of the foreign steel.

Before the duties can be imposed, the International Trade Commission must determine whether these imports are injuring the domestic steel industry. The ITC has until Feb. 4 to make a preliminary determination in the case.

The Commerce Department said it would make its own preliminary determination into the accuracy of the allegations made by U.S. Steel by May 28, with a final decision by Aug. 12.

In addition to the question of whether shipments from the eight countries are being "dumped" in the United States, the Commerce Department said it would investigate whether the governments of Austria, Venezuela and Sweden were unfairly subsidizing steel production in their countries.