Illegal immigrant households tapping into the federal food stamp program are receiving $1.4 billion to $2.1 billion a year despite their ineligibility, according to a new analysis of the Agriculture Department program.

And rules guiding who can get food stamps favor households with illegal immigrants over all-U.S. citizen homes, according to the detailed report from the Center for Immigration Studies released Monday morning.

CIS expert David North has determined that 460,000 to 700,000 households with mix of legal and illegal immigrants are participating in the Supplemental Nutritional Assistance Program, or SNAP.

He said that food stamp benefits average about $255 a month per household, suggesting that the the yearly payout to households with illegals ranges from $1.4 billion to $2.14 billion.

"This looks very much like a billion-a-year problem, and all totally unnecessary," he wrote in the report titled, "An Aid Program that Routinely Discriminates in Favor of Ineligible Aliens.'

To get food stamps, families of three can't earn more than $2,177. But those with an illegal in the household can earn much more. The reason: The USDA prorates total household income to those who are legal.

Here is how North explained it in the report:

Let's say that the all-citizen family consisted of three people, employed father, stay-at-home mother, and a small child. Dad makes $2,400 a month. The family's income is too high for food stamps since the maximum monthly income is $2,177 for a family of three.

Then next door there is a mixed family, also three people, with the father being the only worker, also earning $2,400 a month. The difference is that the father is an ineligible alien and so, under many states' regulations, one-third of the family's income is ignored (prorated is the word in SNAP circles), leaving the family with a nominal income of $1,600 a month that allows the family to get a food stamps allotment, but only for the two citizens, not for all three in the family.

There is thus a band of households of three with earnings in the range of $2,177/mo. at the bottom to $2,589/mo. at the top that would be eligible for food stamps but only if the wage earner is a non-eligible alien in the eyes of USDA; all-citizen households in this band would not be eligible for food stamps. (Here's the math: $2,589 = 150 percent of $1,726, the maximum income allowable for a family of two when there is a 33.3 percent discount on the illegal's wages).

Read his full report here.

Paul Bedard, the Washington Examiner's "Washington Secrets" columnist, can be contacted at pbedard@washingtonexaminer.com