More than 34 million U.S. residents were born outside the United States, with arrivals from Mexico driving much of the growth in the foreign-born population since 2000, a private research group says.

The foreign-born population grew at a clip of over 1 million a year between 2000 and 2004, even though the U.S. economy was suffering, according to the analysis being released Tuesday by the Center for Immigration Studies (search), which favors stricter immigration policies.

That pace was roughly equal to the growth rate between 1996 and 2000, when the economy was on the upswing.

It is more evidence that stricter immigration enforcement after the Sept. 11 attacks did little to stop the influx of immigrants, said Steve Camarota, who wrote the report. Often the worst of economic conditions in America are still better than the financial situations in an immigrant's native country.

"There's a lack of appreciation of the fundamental role of enforcement and failure to understand the limits of bureaucratic capacity," Camarota said of current Bush administration proposals to address immigration.

Immigrants serve a vital need by taking jobs in fast-growing sectors like the construction and service industries, said Roberto Suro, director of the Pew Hispanic Center (search), a nonpartisan research group.

Recent immigrants may be more willing to settle or relocate in areas of the country, where jobs are plentiful, than unemployed people born in the United States, he added.

"I'd be surprised if there was a one-to-one displacement of immigrant and native-born workers," Suro said. "This is a big economy in such a diverse population."

The report comes days after President Bush discussed immigration with Mexican President Vicente Fox and other Latin American leaders in meetings abroad.

Bush renewed a call for Congress to back a proposal he unveiled last year that would allow millions of undocumented laborers to work legally in the United States on temporary visas but would not provide a path to citizenship.

Nearly 10.5 million U.S. residents are from Mexico. That is close to one-third of the total U.S. foreign-born population, up from about one-sixth in 1980.

Overall, more than 9 million immigrants in the United States are illegal, with almost 2 million entering since 2000, Camarota estimated.

The Census Bureau does not ask if someone is in the country illegally. The last estimate of the undocumented population from federal immigration officials, released in 2003, placed the number at 7 million in 2000, most of them Mexican.