Jamieson Greer, the U.S. trade representative, told Congress on Wednesday that a “national emergency” on trade persisted and that the administration remained intent on using tariffs to transform the economy.

The Trump administration is preparing to introduce another barrage of global tariffs as soon as this week, as the president tries to replace tariffs that were invalidated in February by the Supreme Court.

Testifying before the Senate Finance Committee on Wednesday, Mr. Greer said he considered President Trump’s tariff policy a success and would use whatever tools he had available to continue it.

“The specific authorities this administration is using have changed, but the trade strategy has not,” Mr. Greer said. “We are committed to continuing to use tariffs and to negotiate deals to support the reindustrialization of our economy, protect American workers and increase their wages and shrink our trade deficit.”

The Supreme Court in February ruled that Mr. Trump’s use of an international emergency to issue global tariffs last year was unlawful. The decision struck down tariffs Mr. Trump had announced last year on what he called “Liberation Day,” and cast into question the trade deals the administration had negotiated based on those levies. As a stopgap measure, Mr. Trump used another legal measure to impose a flat 10 percent tariff globally. But that tariff is set to expire on Friday.

The administration has already readied a replacement. In June, the Office of the United States Trade Representative proposed imposing a tariff of between 10 and 12.5 percent on goods from more than 80 countries, using a legal authority known as Section 301. It argued that those countries’ failure to impose and enforce laws blocking goods made with forced labor from their markets had unfairly disadvantaged the United States.

The Trump administration is preparing another tranche of tariffs under Section 301 that relates to other countries’ practices toward their factory sectors.

The administration has continued to double down on other tariffs as well. Mr. Trump on Monday signed orders to impose a 50 percent tariff on a wide range of Canadian goods, claiming that Canada had discriminated against the United States in key industries. He said on Tuesday that the United States would impose steep tariffs on generic medications in 2028.

Some analysts speculated that Mr. Trump was trying to force Canada to the negotiating table in talks over the United States-Mexico-Canada Agreement. U.S. and Mexican officials are discussing that deal in Mexico City this week, but talks between the United States and Canada have not officially begun.

On Wednesday, several Republican senators reiterated the importance of the U.S.M.C.A. deal to their states, while Democrats denounced the Trump administration for treating close allies like Canada so harshly.

Ron Wyden, the top Democrat on the Senate Finance Committee, criticized the administration for placing 50 percent tariffs on some Canadian products while rolling “out the red carpet” for China, “one of the biggest trade cheats there is.”

“It just seems to me that on tariffs, the administration has lost the plot,” he said.