Washington ? U.S. immigration agencies say anti-terrorism is their primary mission, but they tried to deport only 12 people on terrorism-related charges from 2004 through 2006, according to a private research study released Sunday.

That group of 12 represents a tiny fraction of the 814,073 people the government tried to remove from the country during those three years. The study’s authors acknowledge the figure understates the anti-terrorism effort by the Homeland Security Department’s immigration agencies.

In addition, because no one knows how many terrorists are in the United States or tried to get in, there is no way to say whether the figure of 12 is too low, too high or about right.

“The right number is unknowable,” co-author David Burnham said in an interview. “But the budget and powers of this agency are influenced by all their talk and rhetoric about terrorism and criminals and if that isn’t what they are doing, it should be considered by Congress and the public.”

Homeland Security spokesman Russ Knocke said the study failed to appreciate record-setting enforcement totals.