By matching inmates' fingerprints to federal immigration databases, authorities hope to pinpoint deportable illegal immigrants before they are released from custody. Inmates in federal and state prisons already are screened. But authorities generally lack the time and staff to do the same at local jails, which house up to twice as many illegal immigrants at any time and where inmates come and go more quickly.

The effort is likely to significantly reshape immigration enforcement, current and former executive branch officials said. It comes as the Obama administration and Democratic leaders in Congress vow to crack down on illegal immigrants who commit crimes, rather than those who otherwise abide by the law.