U.S. citizens are twice as likely to land in New Jersey's prisons as legal and illegal immigrants, according to new data that counter some of the most widely perceived notions about the link between immigration and crime.

Non-U.S. citizens make up 10 percent of the state's overall population, but just 5 percent of the 22,623 inmates in prison as of July 2007, according to an analysis of New Jersey Department of Corrections and U.S. Census data by The Star-Ledger.

As part of the federal government's attempt to fix an immigration system that has allowed deportable criminals to go back on the streets, federal agents started scouring the inmate rolls of New Jersey's state prisons last year.

The goal was to identify criminal aliens so they could be deported once they finished their sentences. That effort yielded another dividend: the first-ever snapshot of the non-U.S. citizen population in New Jersey's state prisons.

The statistics fall directly in line with several other new studies by sociologists that consistently have found the immigrant incarceration rates equal or lower to that of U.S. citizens. The findings contradict one long-held conception about immigrants and crime.

The New Jersey statistics also come to light at a significant juncture, as the U.S. Department of Homeland Security seeks to give local police departments a greater role in enforcing immigration laws in New Jersey and across the country.

"I first got into this because I heard all these terrible complaints that immigrants were a big part of the crime problem," said Anne Morrison Piehl, an economics professor at Rutgers University who has researched incarceration rates among immigrants in California.

"When you look at incarceration rates, you find immigrants much less likely than the native born to be incarcerated," Piehl added. "Once you control for the fact that immigrants are generally younger and less educated, then the data you find is even more surprising."

Advocates of tougher enforcement say the numbers do nothing to lessen the need to crack down on immigrants who commit crimes, including using local police to do it.

"I don't want anyone to think the illegal immigrant population in general causes any more crime than the legal population," said Morristown Mayor Donald Cresitello, who has applied to a federal program to deputize the town's police officers as immigration agents. "That's not my position and statistics show that. But we already have enough of our own criminals and we don't have to invite criminals in."

MYTH OR REALITY?

Immigrant advocates say the numbers are proof that the "illegal immigrant crime wave" touted by anti-immigration groups on television and the internet is more myth than reality.

Several high-profile crimes committed by illegal immigrants, including the slaying of four college students in a Newark schoolyard last August, have fueled such misperceptions, they added.

"It's popular fiction -- and the important word is fiction," said Shai Goldstein, Executive Director of the New Jersey Immigration Policy Network. "It has no foundation in reality as do most of the anti-immigrant arguments which are based on either misperceptions or outright bigotry and sometimes both."

Under tougher immigration laws passed by Congress in 1996, any immigrant, legal or illegal, who is convicted of an aggravated felony may be deported when his or her criminal sentence is completed.

But for years, understaffed federal immigration agencies could not keep up and that pushed many deportable criminals back onto the streets after they got out of jail or prison.

While there is still work to be done in the state's county jails, ICE officials say their efforts to fix the problem in state prisons have been more successful.

From July 2002 to July 2007, the number of state inmates subject to immigration detainers, or holds, more than doubled, from 570 to 1,195, according to data from the New Jersey Department of Corrections.

Detainers, essentially notices that an inmate is not to be released without being turned over to ICE, are issued for both illegal immigrants and legal immigrants who may be stripped of their legal status because of their crimes.

"We've got a handle on the state prisons," said Scott Weber, Newark district director of ICE's Office of Detention and Removal. "I'd be surprised if we were missing people."

Despite the debate over what the data means, it provides the first snapshot of the criminal alien population in New Jersey's 14 state prisons.

Many of them have rap sheets that vividly illustrate the huge holes in the system that allowed criminal aliens to avoid deportation despite repeat arrests and convictions. Still, in almost all categories of crime, they are less likely to be imprisoned than their U.S.-born counterparts.

They account for 86, or 5 percent, of the 1,670 murder charges against state inmates; 27, or seven percent, of the 360 aggravated sexual assaults; and three percent of all drug-related charges. Since many inmates are charged with more than one crime, the number of total convictions exceeds the inmate total.

Non-U.S. citizens account for 11 percent of all sexual assault convictions -- one of the only crimes for which they were equally, or slightly more likely, to be imprisoned than U.S. citizens.

Researchers say the New Jersey statistics fall squarely in line with numerous studies performed in recent years.

A study released earlier this year by Washington-based nonprofit Immigration Policy Center found that U.S.-born men ages 18 to 39 are five times more likely to be incarcerated than are their foreign-born peers.

And, while the number of illegal immigrants in the country doubled between 1994 and 2005, violent crime declined by nearly 35 percent and property crimes by 26 percent over the same period.

Piehl, the Rutgers professor, cited several theories behind the statistics.

The process of immigration, which requires motivation and personal sacrifice, she said, may self-select types of people who are less likely to commit crimes. Once they get here, the harsher penalties immigrants face, namely deportation, also prevents lawbreaking.

Immigration critics say the data paints only part of the picture of the relation between immigration, especially illegal immigration, and crime.

Steven Camarota, research director at the Center for Immigration Studies, a conservative think tank in Washington, D.C, called the New Jersey stats "good news" but cautioned they paint an incomplete picture.

He cited U.S. Border Patrol statistics showing that 15 percent of the illegal border crossers it apprehends have criminal records. He also noted studies that show incarceration rates rise sharply among the children of immigrants.

"There seems to be this silly notion among politicians and researchers that if the incarceration rate is proportional, then that settles the debate," Camarota said. "It isn't just a question of proportionality, it's a question of outrage that people who should not even be in the country and could have been weeded out for previous crimes are here at all."

Brian Donohue may be reached at bdonohue@starledger.com or (973)392-1543.