The result is an enforcement system that poses little threat for tourists, students and others who quietly turn into illegal immigrants, the report says.
Of the 301,046 leads the Immigration and Customs Enforcement agency received in 2004 on possible visa violators, the report says, only 4,164 were formally pursued, resulting in just 671 apprehensions.
And while some of those cases are still pending, the inspector general, Richard L. Skinner, predicted that a "minuscule" number of these individuals were ever likely to face deportation. This action is generally taken only if a person has a criminal history and is detained.
The study estimates that the visa overstay population in the United States is at least 3.6 million people, out of an estimated 9 million to 10 million illegal immigrants. Yet nationally, only 51 full-time agents in the special enforcement unit of the Immigration and Customs Enforcement agency were assigned in 2004 to work on these cases, the report says. Half of the referrals the auditors examined where not followed up within a two-month period.
The unit "could not keep pace with the large volume of lead referrals," the report said, leading the inspector general to question the "effectiveness in identifying, locating and apprehending potential violators."
Responding to the report, Michael J. Garcia, the former director of Immigration and Customs Enforcement, said the agency focused not on how old a lead was, but "its threat or public safety potential," citing, for example, a case that it pursued immediately involving a violator who was also wanted in the rape of a 14-year-old girl.
Many of the leads the agency receives on visa violators also cannot be followed up, Mr. Garcia said, because the individual may have left the country or because the leads are inaccurate. But he did not dispute the report's basic findings.
Just this week, the secretary of homeland security, Michael Chertoff, acknowledged to the Senate Judiciary Committee that his department was not doing enough to prevent illegal immigration.
Conservative Republicans told Mr. Chertoff that before they would support a temporary worker program proposed by President Bush, Mr. Chertoff must do a better job of preventing people from illegally crossing the borders or ignoring immigration laws after arriving legally in this country. The Bush program would give legal status for up to six years for certain illegal immigrants already working in the country.