The International Trade Commission yesterday questioned the nation's steel producers on the validity of recently giving the United Steelworkers union the "richest contract in the history of the union" at a time when it is complaining of being injured by foreign steel imports.

The questioning marked the first of two days of polite attacks between the domestic steel industry, led by U.S. STeel which filed the dumping complaints, and producers from seven European countries accused of selling certain steel products here at prices below their fair values.

The politically-sensitive hearings, pitting the U.S. companies against those of U.S. allies, could become the basis for an international trade war. tAnd both sides in the showdown are heavily armed with lawyers, charts, figures and sob stories. While the domestic producers fired away yesterday, the opposition patiently waited for their turn to fight back today.

For the past few months the Carter administration has attempted to dissuade U.S. steelmakers from filing dumping complaints against U.S. allies because they could lead to an increase in international tensions. Commerce Sec. Philip M. Klutznick last week, after stating the government will begin its dumping investigation, emphasized the administration's hope that the complaints of the nation's largest steelmaker can be solved by other means.

"The administration remains open to pursuing any of the legal alternatives to find solutions in genuine cooperation with industry, labor and our trading partners," Klutznick said.

U.S Steel, however, is forging ahead.

The hearings, conducted by the ITC's director of operations, Charles W. Ervin, and its staff, will recommend to the commission whether there is a reasonable indication that injury to a domestic industry exists from dumping.

Ervin asked U.S. Steel representatives whether the steel industry had control of the recently negotiated steelworkers' wage package and if, in granting the pay raises, U.S. Steel and the domestic industry had acted as though they are being injured by imports. The contract maintains the steelworkers as the nation's highest paid industrial workers.

U.S. Steel representatives said that a large part of the wage rise was due to inflation and cost of living increases and blamed the government for being ineffective in reducing inflation, which caused higher labor costs.