WASHINGTON — Vice President Mike Pence and other top administration officials will meet Wednesday with Mexico’s top diplomat as both sides try to avert the potentially crippling economic consequences of President Trump’s threat to impose tariffs on all Mexican imports.

Mr. Trump has vowed to impose a 5 percent tariff on all goods from Mexico beginning Monday and to increase the tax to 25 percent by October if Mexico does not prevent migrants from illegally entering the United States. On Tuesday, Mr. Trump said that it was “more likely that the tariffs” would be imposed. But on Wednesday, the president said he believed Mexico was ready to make a deal to prevent the tariffs from going into effect.

”Mexico, you know, wants to make a deal,” Mr. Trump said during a trip to Ireland. “They have their entire delegation right now going over to probably the White House location to negotiate with our people.”

Mexican officials, along with Republican lawmakers, are trying to prevent Mr. Trump from imposing tariffs on Monday, as he has threatened. Marcelo Ebrard, the Mexican foreign minister, is scheduled to meet on Wednesday afternoon at the White House with Mr. Pence, a senior administration official said, in an effort to convince the president that Mexico is doing everything it can to help prevent illegal immigration across the United States border. Secretary of State Mike Pompeo and Robert Lighthizer, the United States Trade Representative, were also expected to attend the meeting.

Mr. Trump, frustrated by what he views as Mexico’s failure to stem the flow of migrants, said he would use broad emergency powers to impose punishing tariffs on the country. But top American officials have spoken in vague terms about what steps Mexico must take, and it remains unclear exactly what Mexico could do to persuade Mr. Trump to back down.

Peter Navarro, a top trade adviser who has advocated using levies to punish Mexico, said in an interview with CNN on Wednesday that Mr. Trump’s threat had gotten the Mexican government’s attention and that the United States might not have to impose the tariffs.

“We believe that these tariffs may not have to go into effect precisely because we have the Mexicans’ attention,” Mr. Navarro said

He outlined several things that Mexico must do to prevent the tariffs, including committing to taking “all the asylum seekers and applying Mexican laws which are much stronger than ours.”

He also urged Mexico to do more to secure its border with Guatemala and tighten check points for migrants within Mexico.

Mr. Ebrard has also expressed optimism, telling reporters on Tuesday in Washington that there was an 80 percent chance that Mr. Trump would not impose the tariffs.

But others in Washington were more doubtful that the two sides could come to a resolution before Monday’s deadline. Carlos Heredia, a professor at the Centro de Investigación y Docencia Económicas in Mexico City, said Tuesday that whatever action Mexico takes to prevent migration into the United States, it was unlikely to satisfy the president.

“If there is any logic to the way that President Trump handles policy, it’s that he likes conflict,” Mr. Heredia said. “I don’t think that there is a way to please Trump.”

Others said that it would take time for Mexico to make the changes the Trump administration was requesting.

“This is not going to happen in seven days,” said Arturo Sarukhan, a former Mexican ambassador to the United States. “You can’t enforce your way out of a migration crisis.”

Mr. Trump’s threat to tax Mexican products has rattled financial markets and prompted an outcry from businesses that would be affected, including automakers, agricultural companies and retailers. The chairman of the Federal Reserve said on Tuesday that the central bank was watching Mr. Trump’s trade war warily and would act to prevent economic damage from the conflict.

Businesses are also worried that the president’s move risks derailing what would be his signature trade achievement: passing the newly negotiated North American trade agreement.

The United States-Mexico-Canada Agreement was signed last year, but it still needs to be ratified by legislators in all three countries. Mexico submitted the text to its Senate hours before Mr. Trump’s threat. But Mexican officials are unlikely to move forward with that vote with the threat of tariffs hanging over them.

Mr. Ebrard, who has been in Washington all week meeting with Trump administration officials and members of Congress, said earlier in the week that Mexico was already enforcing its own immigration laws but argued that there was more the countries could do to work together. He said Mexican officials had come to Washington ready to “design actions together.”

Kevin McAleenan, the acting secretary of homeland security, repeated the administration’s demands in an interview with The Hill published on Tuesday. He said Mexico must crack down on illegal crossings from Guatemala, and use American intelligence to target smuggling operations that try to sneak migrants across the border.

Mr. McAleenan also said the administration expects Mexico to help tighten the shared border, even though the Mexican government has agreed to take in migrants while their asylum cases are processed in the United States.

“We can’t have the situation where 1,000 people in one group can cross the border at 4 a.m. without any interdiction or any effort to stop that unlawful activity,” said Mr. McAleenan, citing a group that illegally crossed last week into El Paso. The group of 1,036 migrants was the largest ever recorded by the Department of Homeland Security to cross illegally into the United States.

But Mexico has maintained that it is already taking action to stem the flow of migrants.

Mexico’s ambassador to the United States, Martha Bárcena, said in a press conference Monday that without Mexico’s efforts, many more migrants would be arriving at American borders.

“There is a clear limit to what we can negotiate,” Ms. Bárcena said. “And that limit is Mexican dignity.”

On Tuesday, Mr. Ebrard met for a half-hour with Speaker Nancy Pelosi and several other Democratic lawmakers.

Republican senators are also mobilizing to prevent the White House from moving ahead with tariffs, warning Mr. Trump on Tuesday that they were almost uniformly opposed to his plans to tax Mexican imports.

Several big states would be hit hard by the proposed tariffs on Mexican products, including Texas, Michigan, California, Illinois and Ohio, according to the U.S. Chamber of Commerce.

“We’re holding a gun to our own heads,” said Senator John Cornyn, Republican of Texas.

Officials at Customs and Border Protection were making preparations on Wednesday to begin imposing the tariffs just after midnight on Monday morning.

In an interview, a Customs spokesman said the department was waiting for Mr. Trump to issue a presidential proclamation, which would then by followed by a Federal Register notice, outlining the basis for the tariffs and the universe of Mexican products to which they would apply. But even without a formal order establishing the tariffs, Customers workers are already building up the informational technology infrastructure needed to apply the tariffs on Monday morning to importers bringing in goods from Mexico.

Officials said they were readying technical guidance for importers, to help them properly fill out paperwork and pay the appropriate tariff — and preparing to assist those importers who have grown accustomed to paying no tariffs under the terms of the North American Free Trade Agreement.

They also said administration officials are still discussing whether there will be exemptions for certain industries from the tariffs, and whether there will be a formal process for American companies to apply for tariff exclusions for certain products they import, as was the case with steel and aluminum tariffs and some tariffs on products from China.