Mr. Ross described the effect of the tariff as “a fraction of a penny on a can of beer.” Mr. Navarro clashed with Chris Wallace of Fox News, who tried to get the economic adviser to admit that those costs, when multiplied by all products that use steel and aluminum over the entire economy, would escalate into the billions of dollars. Mr. Navarro said he saw the costs as “insignificant” in the mission to preserve the steel and aluminum industries, which have seen factories pick up and move from the United States to cheaper parts of the world.

The White House’s plan continued to face fierce criticism, including from Republicans who believe free trade is in the interest of the economy.

Senator Lindsey Graham, Republican of South Carolina, criticized the tariffs for falling more heavily on American allies than on China, which he said had earlier flooded the global market with steel.

Economists say the tariffs, if applied without exceptions, would harm allies like Canada, South Korea and the European Union, which export more steel to the United States than China does. Shortly after the tariffs were announced, the European Union responded by saying that it was already preparing to levy retaliatory tariffs on American products, including orange juice, bluejeans and Harley-Davidson motorcycles.

“You’re letting China off the hook,” Mr. Graham said on CBS’s “Face the Nation.” “China wins when we fight with Europe.”

Joshua B. Bolten, the head of the Business Roundtable and chief of staff in the George W. Bush administration, called the tariffs “a huge mistake.”

Speaking on “Fox News Sunday,” Mr. Bolten acknowledged that the president was trying to fulfill his campaign promises and help American workers in the steel and aluminum industries. But Mr. Bolten said the tariffs would cause “huge damage across broad sectors of the economy” that use steel and aluminum in their products, or that face retaliation from angry trading partners.