Tom Homan, President Trump’s chief border official, cast the operation largely as one to help ease long security lines. The Homeland Security Department said 14 airports across the country would be involved.

Tom Homan, the White House border czar, confirmed on Sunday that Immigration and Customs Enforcement agents would be deployed to U.S. airports on Monday, casting the operation largely as an effort to ease long lines that have caused frustration among travelers during one of the busiest travel seasons.

ICE personnel, including agents from Homeland Security Investigations, are planning to be at 14 airports, according to a document obtained by The New York Times. The airports span the country, including Kennedy and LaGuardia in New York, Newark, Philadelphia, Chicago, Atlanta, New Orleans, Houston and Phoenix.

The agents are expected to conduct tasks to free up Transportation Security Administration agents to handle processing travelers, according to an official from the Homeland Security Department, who spoke on the condition of anonymity because he was not authorized to discuss the location of ICE agents.

President Trump announced the measure on Saturday, first as a threat aimed at pressuring congressional Democrats to agree to a deal to fund the Homeland Security Department, which includes the T.S.A., and then as an aggressive operation. He said on social media that agents would “do security like no one has ever seen before,” which would include “the immediate arrest of all illegal immigrants who have come into our Country.”

In an interview on CNN’s “State of the Union” on Sunday, Mr. Homan said that his agency was drawing up plans for deployment and stressed that ICE agents would help support security officials whose ranks have thinned as thousands have gone without pay amid a partial government shutdown.

“It’s a work in progress, but we will be at airports tomorrow, helping T.S.A. move those lines along,” Mr. Homan said.

The Homeland Security Department said in a statement on Sunday night that the deployment was necessary because of long lines for screening passengers, and it placed the blame on Democrats. But it did not give details about what agents would do at the airports.

“Because of the Democrat shutdown, President Trump is using every tool available to help American travelers who are facing hours long lines at airports across the country — especially during this spring break and holiday season that is very important for many American families,” the statement said, adding: “This will help bolster T.S.A. efforts to keep our skies safe and minimize air travel disruptions.”

With the deployment less than 24 hours away, administration officials apparently have not nailed down many details. Mr. Homan said that “his opinion” was that agents would concentrate on airports with long wait times at security, prioritizing ones with lines of about three hours. He said that agency heads were still discussing how many agents to deploy, how quickly to deploy them and to where.

He said more concrete plans would be made on Sunday afternoon.

“When we deploy them more, we’ll have a well-thought-out plan to execute,” Mr. Homan said.

Airports around the country have been smothered with passengers over the past weeks, hit with the combination of the shutdown and heavy spring break travel. At LaGuardia Airport in New York on Sunday, the wait in the line at T.S.A. checkpoints was as long as three hours.

Sarah Estes, 41, a nurse from Dallas visiting for what she called a “girls’ trip,” said the airport website had estimated a 20-minute wait for T.S.A. PreCheck. But after they arrived, she said, they were told it would take at least two and a half hours.

Ms. Estes said she had conflicting thoughts about using ICE at the airports.

“I don’t trust those people,” she said. “So how can I trust them to help out at the airport? But the airports do need help.”

Mr. Homan noted that ICE agents were already working in airports, doing immigration enforcement and conducting investigations into reports of criminal activity like smuggling. He also said that the ICE agents — who are still being paid while T.S.A. agents are not — were “well trained” in security and identification.

But he indicated that the bulk of their work would be to cover exits and other areas that T.S.A. workers are now staffing in order to free up agents to do screenings and other functions to help reduce lines.

“This is about helping T.S.A. do their mission, and get the American public through that airport as quick as they can, while adhering to all the security guidelines and the protocols,” he said. “We’re simply there to help T.S.A. do their job in areas that don’t need their specialized expertise.”

Representative Hakeem Jeffries, Democrat of New York and the minority leader, blasted Mr. Trump’s idea on Sunday.

“The last thing the American people need is for untrained ICE agents to be deployed at airports across the country, potentially to brutalize or to kill them,” he said during an interview on “State of the Union,” referring to the killings of two American citizens in Minneapolis in January.

Mike Gayzagian, a T.S.A. officer at Boston Logan International Airport and the president of the American Federation of Government Employees Local 2617, which represents T.S.A. employees across New England, said he was unsure whether ICE agents would show up to airports in his region on Monday. If they did, he said, they were not likely to be of much help, especially if they were stationed at exits as Mr. Homan suggested.

Mr. Gayzagian said the administration’s move shifted attention from the larger issue at hand. “None of this would be happening if Congress had just simply decided to pay us,” he said.

Johnny Jones, a T.S.A. officer at Dallas Fort Worth International Airport and a secretary-treasurer with the American Federation of Government Employees, the union representing nearly 50,000 T.S.A. officers, said that stationing ICE agents at airports would “be a distracting scenario, to say the least.”

He said ICE agents’ presence could make airports less safe because of the widespread public anger at immigration officers’ recent conduct. He added that placing paid immigration agents next to unpaid T.S.A. agents would inflame frustrations.

“All we want is a paycheck,” Mr. Jones said. “We don’t need all these optics.