By MIRIAM JORDAN

The Department of Homeland Security said Friday it was revising a program that authorized local police to enforce federal immigration law -- a controversial aspect of U.S. border policy.

The new guidelines sharply reduce the ability of local law enforcement to arrest and screen suspected illegal immigrants. They are intended to prevent sheriff and police departments from arresting people "for minor offenses as a guise to initiate removal proceedings," according to Homeland Security. The program will instead focus on more serious criminals.

"In a world of limited resources, our view is that we need to focus first and foremost on people committing crimes in our community who should not be here," said John Morton, Assistant Secretary of U.S. Immigration and Customs Enforcement. Mr. Morton said his agency would sign new contracts with local law enforcement that would bolster federal oversight.

In the past two years, more than 120,000 suspected illegal immigrants were identified through the program, and most ended up in deportation proceedings. By comparison, ICE removed 356,739 illegal immigrants from the U.S. during the fiscal year ended Sept. 30, 2008 -- a 23.5% increase over the 2007 total.

"If I'm told not to enforce immigration law except if the alien is a violent criminal, my answer to that is we are still going to do the same thing, 287g or not," said Mr. Arpaio. His deputies have identified in jail or picked up on the streets more than 30,000 illegal immigrants in the Phoenix area. "We have been very successful," said the five-term sheriff.

The Department of Justice is investigating whether Mr. Arpaio's deputies have used skin color as a pretense to stop Latinos suspected of being illegal immigrants.

Mr. Obama's policy change is expected to bolster his standing with Latinos and some Democratic legislators. The administration is seeking to set the stage for a sweeping overhaul of immigration legislation that could put millions of illegal workers on the path to U.S. citizenship.

President George W. Bush pursued a similar goal. After the efforts failed in Congress, his administration stepped up enforcement with raids and the expansion of such programs as 287g.

The provision was created by Congress in 1996 and designed to train local police to help federal immigration authorities locate criminal aliens. It took six years for the first state, Florida, to sign on to the program.

The Bush administration promoted the program among sheriffs and police chiefs, turning it into a symbol of his crackdown on illegal immigration.

Since January 2006, more than 1,000 state and local law-enforcement officials have been certified. Many jurisdictions used those officers in jails, where they could sort through many inmates in a single shift.

Southern states account for more than 40 of the 66 existing participants. There are 42 applications pending, most of them in the South. Both Virginia and North Carolina, where the Latino immigrant population has grown, each have nine 287g agreements, more than other states.

"I think the program is working great," said Wake County, N.C., Sheriff Donnie Harrison. "If the highway patrol brings someone to our jail, and they say they are foreign born, then they are flagged for 287g. They have committed a violation of some sort to be brought to our jail...from broken tail lights to murder and rape."

Raleigh, N.C., resident Maria Hernandez was booked into a Wake County jail after failing to show up for her 6-year-old son's truancy hearing, according to her account and that of her attorney, Marty Rosenbluth.

Ms. Hernandez, a cleaning lady who came to the U.S. illegally nine years ago, is now in deportation court. "I don't understand why they come after people like me," she said.

Homeland Security Secretary Janet Napolitano ordered a comprehensive review of 287g shortly after taking her post earlier this year. Members of Congress and the Government Accountability Office had raised concerns the program was being used "to process individuals for minor crimes, such as speeding, contrary to the objective of the program."

The shift on 287g follows other recent modifications to immigration policy by the Obama administration, reflecting an effort to shift the burden of immigration enforcement to employers, while making it difficult for illegal immigrants to get hired.

In the past two weeks, Ms. Napolitano said federal contractors would be required to check the identity of new hires against a federal database. DHS also will audit hundreds of companies to verify whether their employees are eligible to work.

Write to Miriam Jordan at miriam.jordan@wsj.com