WASHINGTON — Teams assigned to make sure foreigners facing departure orders actually leave United States have a backlog of more than 600,000 cases and cannot accurately account for the fugitives' whereabouts, the government reported.

The report by the Homeland Security Department's inspector general found that the effectiveness of teams assigned to find the fugitives was hampered by "insufficient detention capacity, limitations of an immigration database and inadequate working space."

Even though more than $204 million was allocated for 52 fugitive operations teams since 2003, a backlog of 623,292 cases existed as of August 2006, the report said.

The number of illegal immigrants in the United States has been estimated at between 11.5 million and 12 million. About 5.4 percent of them are believed to be "fugitive aliens," those who have not obeyed orders to leave the country.

The inspector general found there is too little bed space available to detain such fugitives, and agents are hampered by an inaccurate database. Another factor that limits the teams' effectiveness is insufficient staffing, the report said