“They might drive down slightly the wages of roofers in the United States,” Mr. Lazear said. “But as a result of having this valuable supply of labor from abroad, other people on the construction project like carpenters and electricians are more productive. They have better people to work with, more people to work with. The cost of doing the job is lower, and some of that is passed on to consumers in the form of lower prices.”

The study reinforces President Bush’s campaign for a comprehensive immigration bill that calls for more border security, a guest worker program and a “merit-based system” of selecting immigrants that emphasizes education and job skills. The bill, pending in the Senate, would also offer legal status and work permits to most of the estimated 12 million illegal immigrants in the United States.

Many Democrats say the bill could depress the wages of American workers. Senator Byron L. Dorgan, Democrat of North Dakota, said the guest worker program would “put downward pressure” on the wages in construction, manufacturing and other industries.

The White House is entering a debate that has been raging for years.

In one study, George J. Borjas, a professor of economics at Harvard, found that “by increasing the supply of labor between 1980 and 2000 immigration reduced the average annual earnings of native-born men by an estimated $1,700, or about 4 percent.”

Image Edward P. Lazear, whose Council of Economic Advisers issued a report praising immigrants role. Credit... Carol T. Powers/Bloomberg News

“Among natives without a high school education, who roughly correspond to the poorest tenth of the work force,” Professor Borjas said, “the estimated impact was even larger, reducing their wages by 7.4 percent.”