But about one-third of those family members who received green cards since 2000 had college degrees, Mr. Peri said. “People have an outdated image” of legal immigration, he said. “It’s mostly Asian, Indian, Chinese people who are coming to do mid- and high-level professional jobs.”

George J. Borjas, the Harvard immigration economist whose work is the only evidence that the administration has cited as justifying its proposals, said in an interview on Wednesday that there was no economic justification for reducing skilled immigration.

“That is a political decision,” he said. “That is not an economic decision.”

The economic impact of low-skilled immigration is more hotly debated. Mr. Borjas is the foremost proponent of the view that low-skilled immigration reduced the incomes of American workers without high school degrees. He estimates the total impact at 3 percent to 5 percent of income over the last two decades.

Economists agree that other factors, notably technological improvements, are primarily responsible for the broader deterioration in the fortunes of the American working class.

Mr. Borjas also argues that low-skilled immigration does not produce clear benefits for the economy as a whole. He said that the benefit of low-cost labor was offset, or even slightly outweighed, by the cost of providing government services to immigrants.

The primary beneficiary of immigration is the immigrant, Mr. Borjas said.

“If all you care about is economics, then it’s really clear,” he said. “But do you want to live in a country that only cares about money, or do you want to live in a country that has a legacy of being generous to immigrants? Maybe you want a compromise.”