On Jan. 7, the day that the U.S. Senate opened the impeachment trial of President Clinton, the President, in a long-awaited report to the House and Senate, effectively told Japan to slow the flow of its steel exports to the U.S. The Clinton administration also proposed a relatively minor change in U.S. tax laws to benefit steel companies that have been losing money. The Administration hopes its moves will assuage the U.S. steel industry, which in recent months has mounted a high-visibility campaign against a surge of shipments from Japan, Russia, South Korea, and Brazil. The President pledged to consider other actions as circumstances warrant. But those possibilities apparently do not include a formal call for so-called voluntary restraint agreements, which are barred by current international trading rules.