EVERY year thousands of immigrants being held on Rikers Island are transferred to federal custody and deported. Only about half of them have a criminal record, many of them are here legally, most of them have their due process rights violated and all of them are subjected to substandard conditions before being returned to their countries of origin.

The city has no obligation to hand over detainees, and in fact many cities around the country have refused to participate in the federal government’s efforts. Mayor Michael Bloomberg should do the same.

Under what is known as the Criminal Alien Program, for more than a decade city law enforcement officials have given the Immigration and Customs Enforcement agency the names of all arrestees, regardless of the crime they are accused of committing and regardless of whether they are convicted. When agents locate an immigrant, they often request that he be transferred to federal custody.

Once in federal hands, most detainees are transported to centers in Texas and Louisiana, far from their families. Conditions at these federal detention centers are worse than those at many prisons, with inadequate medical care and access to phones and legal materials. Detainees are subjected to abuse and sometimes even death — 107 people died in immigration detention from 2003 to 2010.

True, earlier this year the federal government proposed upgrading these centers, including those in the New York region, to increase capacity and improve conditions. But this is a Band-Aid solution to a much larger problem: over 80 percent of those in detention have little or no access to lawyers — and no effective way to represent their interests in a surreal, confusing system.

Not only is the program an injustice — according to our calculations, it has cost the city tens of millions of dollars. New York houses these prisoners at Rikers far longer than it would otherwise, because of a misguided city policy which forbids anyone with immigration holds — meaning they might be placed in deportation proceedings — from being released on bail.

What’s more, because of its flaws and draconian rules, the city’s policy deters many immigrant New Yorkers from reporting crimes, fearing that contact with the police could lead to deportation.

Perhaps what is most disturbing is that sometimes legal immigrants who have been convicted of no crime are caught up in this system. Their plight stems partly from flaws in federal databases; the process is too rushed to ensure proper identification of status and identity, let alone confirmation of criminal background.

But it’s also a matter of political pressure to increase the number of people who are deported every year. E-mails released in December from the Department of Homeland Security showed how the immigration agency has been pushing states and cities to send it the fingerprints of all those they arrest as part of a similar program, Secure Communities.

For all these reasons, Mayor Bloomberg should end New York’s collaboration with federal officials on Rikers Island and resist Washington’s pressure to join the newer Secure Communities program. New York wouldn’t be the first: communities as diverse as Santa Clara, Calif., and Arlington, Va., have limited or prevented federal access to their jails.

For decades, New York City has been a beacon to the rest of the country in promoting immigrant rights. We must not let our desire to enforce immigration laws lead us to dim that light.