The report by Syracuse University's Transaction Records Clearing House (TRAC) is causing some to question the effectiveness of immigration enforcement.

"We found a very surprising thing," said Dr. Sue Long of Syracuse University, TRAC director and co-author of the report.

Long and her colleagues found nearly 31 percent of deportation cases were thrown out last year nationally -- up from 25 percent in 2009.

"Something was changing and they were being much less successful," Long said, referring to Immigration and Customs Enforcement (ICE).

The report found 63 percent of deportation cases in Los Angeles were thrown out in 2010 -- up from 27 percent in 2008.

In San Diego, the rejection rate went from 27 percent in 2008, to 32 percent in 2009, to 43 percent in 2010, according to the report.

"This administration is enforcing the rule of law," Homeland Security Secretary Janet Napolitano said last October. "We are enforcing the immigration laws. The numbers that need to go up are going up. The numbers that need to go down are going down."

Immigration and Customs Enforcement officials would not comment on the report but issued the following statement: "It appears that the report fails to take into account many factors, including the fact that immigrations courts are independently authorized to allow illegal aliens to remain in the United States."

Long said the government won't provide any detail about the cases that were thrown out or why the courts may have allowed those in the country illegally to stay.

"They said no. They did not want to release that information," Long said. "If you're not successful in the end in deporting people, then that's hardly achieving your stated goals."