President Trump has settled on a final plan for sweeping “reciprocal” tariffs, which are expected to take effect on Wednesday after he announces the details at an afternoon Rose Garden ceremony.

The White House press secretary, Karoline Leavitt, confirmed the timeline in a briefing with reporters on Tuesday, adding that Mr. Trump had been huddling with his trade team to hash out the finer points of an approach meant to end “decades of unfair trade practices.”

When pressed on whether the administration was worried the tariffs could prove to be the wrong approach, Ms. Leavitt struck a confident note: “They’re not going to be wrong,” she said. “It is going to work.”

The administration has been weighing several different tariff strategies in recent weeks. One option examined by the White House is a 20 percent flat tariff on all imports, which advisers have said could help raise more than $6 trillion in revenue for the U.S. government.

But advisers have also discussed the idea of assigning different tariff levels to countries depending on the trade barriers those countries impose against American products. They have also said that some nations might avoid tariffs entirely by striking trade deals with the United States.

Speaking to reporters in the Oval Office on Monday, Mr. Trump said the United States would be “very nice, relatively speaking,” in imposing tariffs on a vast number of countries — including U.S. allies — that he believes are unfairly inhibiting the flow of American exports.

“That word reciprocal is very important,” Mr. Trump told reporters. “What they do to us, we do to them.”

By Tuesday, Ms. Leavitt said the president had made a decision and was with his trade team now “perfecting it.” When asked if companies could do anything to avoid the tariffs, Ms. Leavitt said the president was “always up to take a phone call” from companies but was “very much focused on fixing the wrongs of the past.”

She also said that many foreign governments had called the president and his team to talk about the tariffs, but that Mr. Trump was focused on the interests of the United States.

“The president has a brilliant team of advisers who have been studying these issues for decades, and we are focused on restoring the golden age of America and making America a manufacturing superpower,” she said.

The prospect of tariffs has left markets uneasy. Stocks edged down at the start of trading, with the S&P 500 opening about 0.4 percent lower before rebounding after a choppy day Monday that ended with the index registering its worst month and quarter since 2022.

Investors are still seeking clarity on the scope of Mr. Trump’s reciprocal tariffs, and the economic uncertainty surrounding a global trade war has fueled stock market volatility in recent weeks.

It has similarly troubled the manufacturing industry, which showed signs of contraction in March, according to data released Tuesday from the Institute for Supply Management, which is closely tracked by the White House. The report found declines in employment and new orders, as firms raised alarms about the nature of Mr. Trump’s tariffs and the prospect for costly global retaliation.

The president is set to receive reports from his advisers on nearly two dozen trade-related topics on Tuesday, advising him on how he might proceed on addressing a range of issues.

The reports, which are due from the Commerce and Treasury Departments as well as the Office of the United States Trade Representative, will look at the causes of persistent trade deficits, unfair trade practices by other countries, gaps in existing trade agreements and recommendations for achieving reciprocity in trade relationships, among other issues.

The trade representative, for example, was responsible for identifying countries with which the United States should negotiate new trade agreements, and whether China has upheld its commitments under a 2020 trade deal that Mr. Trump signed in his first term.

In several cases, Mr. Trump has acted before even seeing the details of the reports. Although he asked for reviews into whether foreign metals posed a risk to national security, Mr. Trump has already imposed 25 percent tariffs on steel and aluminum imports. He also hit Canada, Mexico and China with tariffs intended to stem the flow of fentanyl and migrants into the United States, which is another area that his administration was studying.

How Mr. Trump plans to proceed on Wednesday remains an open question — one that has left America’s trading partners struggling to determine a response.

The European Union has already announced that it will respond to Mr. Trump’s steel and aluminum tariffs with countermeasures. But European officials are still contemplating how to respond to the tariffs that Mr. Trump will unveil on Wednesday.

Although the European response so far has concentrated on imposing higher tariffs on a wide variety of goods — whiskey, motorcycles and women’s clothing are among the products that could be affected — officials are also open to placing trade barriers on services, using a new trade weapon that was developed only in 2021.

That tool could be used to hit big tech firms, said two diplomats familiar with the matter but who spoke on condition of anonymity to discuss internal deliberations. That means that instead of affecting physical goods, it could have an impact on companies like Google, Meta or even American banks.

The goal would be to give the European Union more leverage, since Europe buys more services from the United States than it exports — making its market, and access to European consumers, a potentially powerful tool. But no decisions have been made.

“Europe holds a lot of cards,” Ursula von der Leyen, the president of the European Commission, said during a speech on Tuesday. “From trade to technology to the size of our market.”

Officials are emphasizing that their goal is still to negotiate, though they will respond firmly if needed.

“All instruments are on the table,” Ms. von der Leyen said.

Danielle Kaye contributed reporting.