WASHINGTON — A report Wednesday indicating a marked decline in the number of illegal immigrants in the U.S. fueled a widening national debate over the Bush administration's policy of immigration enforcement through aggressive workplace raids.
The largest such enforcement action was in May in Postville, Iowa, where federal immigration agents descended on a meatpacking plant and arrested nearly 400 workers later detained in a building used to house cattle.
The administration began aggressively enforcing workplace laws after Congress last year failed to pass an immigration overhaul. In the months since, thousands of workers have been arrested in scores of raids.
Conservatives have applauded the tactics, while critics have pointed to mistaken arrests of U.S. citizens, deaths of immigrants in detention and limited scrutiny of managers who recruit and hire them.
However, evidence that the strategy may have succeeded in reducing the number of illegal immigrants was presented in a report Wednesday by a group favoring tighter curbs on all forms of immigration.
The report by the Center for Immigration Studies, a Washington-based think tank, says that the number of illegal immigrants fell about 11% between last August and May, from 12.5 million to 11.2 million.
The study was based on an analysis of census data and concludes that if that rate of decline is sustained, the number of illegal immigrants will be halved in five years.
Steve A. Camarota, the center's research director, acknowledged that the economy played a role in the decline but said that several factors pointed to enforcement as key. For instance, the legal immigrant population continues to grow, while the fall-off in illegal immigrants began even before unemployment began rising.
"It seems that increased enforcement has played a significant role," Camarota said.
Camarota also said the data suggested that many illegal immigrants were leaving of their own accord. The decline in their number is much larger than the tally of those removed by the government, the report says.
"It challenges the idea that there is no way to deal with the problem but for creating some kind of legal status [for illegal immigrants]," Camarota said. "And it seems you don't have to deport everyone."
Independent demographers said they also had seen a drop in the illegal immigrant population. But some questioned the study's methodology, decline figures and underlying assumptions.
