Less than two days before the Trump administration plans to impose steep tariffs on imported steel and aluminum, its chief trade representative said Wednesday that several of the nation’s top trading partners were in line for potential exemptions.

The trade official, Robert Lighthizer, said at a hearing of the House Ways and Means Committee that the administration was talking with Australia, Argentina and the European Union about excluding them from the 25 percent tariff on imported steel and 10 percent charge on aluminum.

He added that there were plans to talk with Brazil about possible exemptions, and raised the possibility that South Korea could be excluded as the United States continues to hold talks with Seoul over a bilateral trade agreement.

Mr. Lighthizer said he favored sparing those countries from the tariffs while talks continue, though he said that decision would be “up to the president.” Mr. Lighthizer said he expected the conversations over exclusions to conclude by the end of April.