“As we have noted for years, in jurisdictions where we are not allowed to assume custody of aliens from jails, our officers are forced to make at-large arrests of criminal aliens who have been released into communities,” he said. “When sanctuary cities release these criminals back to the street, it increases the occurrence of preventable crimes, and more importantly, preventable victims.”

But Gil Kerlikowske, the former commissioner of C.B.P., which oversees tactical units along the border, said sending the officers to conduct immigration enforcement within cities, where they are not trained to work, could escalate situations that are already volatile. He called the move a “significant mistake.”

“If you were a police chief and you were going to make an apprehension for a relatively minor offense, you don’t send the SWAT team. And BORTAC is the SWAT team,” said Mr. Kerlikowske, who is a former chief of police in Seattle. “They’re trained for much more hazardous missions than this.”

It was a gun-wielding BORTAC agent who, in April 2000, seized Elian Gonzalez — a Cuban boy who was embroiled in an international asylum controversy — from his uncle’s arms after agents had forced their way into the home where the boy was staying.

The Border Patrol squads will be charged with backing up ICE agents during deportation operations and standing by as a show of force, the officials said.

ICE agents typically seek out people with criminal convictions or multiple immigration violations as their primary targets for deportation, but family members and friends are often swept up in the enforcement net in what are known as “collateral” arrests, and many such people could now be caught up in any enhanced operations.

ICE leadership requested the help in sanctuary jurisdictions because agents there often struggle to track down undocumented immigrants without the help of the police and other state and local agencies. Law enforcement officers in areas that refuse to cooperate with ICE and the Border Patrol — which include both liberal and conservative parts of the country — often argue that doing so pushes undocumented people further into the shadows, ultimately making cities less safe because that segment of the population becomes less likely to report crimes or cooperate with investigations.