WASHINGTON, March 21 (Reuters) – The United States is in talks with the European Union, Argentina and Australia on granting possible exemptions to steel and aluminum tariffs, Trade Representative Robert Lighthizer told the House Ways and Means Committee in a hearing on Wednesday.  Lighthizer said that talks with South Korea over any possible exemption would be carried out within the context of existing trade negotiation talks with Seoul. The U.S. has already granted exemptions for Canada and Mexico from the tariffs which were imposed earlier this month by President Donald Trump.