WASHINGTON – The Obama administration said Thursday it will allow many illegal immigrants facing deportation the chance to stay in this country and apply for a work permit, while focusing on removing from the U.S. convicted criminals and those who might be a national security or public safety threat.

That will mean a case-by-case review of approximately 300,000 illegal immigrants facing possible deportation in federal immigration courts, Homeland Security Secretary Janet Napolitano said in announcing the policy change.

Advocates for an immigration overhaul have said that the administration, by placing all illegal immigrants in the same category for deportation, has failed to live up to its promise to only deport the “worst of the worst,” as President Barack Obama has said.

“From a law enforcement and public safety perspective, DHS enforcement resources must continue to be focused on our highest priorities,” Napolitano wrote a group of senators supporting new immigration legislation. “Doing otherwise hinders our public safety mission — clogging immigration court dockets and diverting DHS enforcement resources away from the individuals who pose a threat to public safety.”

Some states are rebelling against another administration effort to control illegal immigration known as Secure Communities. The program requires that when state and local law enforcement send criminal suspects’ fingerprints to the FBI, the prints are run through an immigration database to determine the person’s immigration status. States have argued that the program puts them in the position of policing immigration, which they consider a federal responsibility.

In June, the director of Immigration and Customs Enforcement, John Morton, sent a memo to agents outlining when and how to use discretion in immigration cases. It also covered those potentially subject to a legislative proposal intended to give young illegal immigrants who go to college or serve in the military a chance at legal status.

Morton also suggested that agents consider how long someone has been in the United State, whether that person’s spouse or children are U.S. citizens and whether that person has a criminal record.

A senior administration official said delaying deportation decisions in cases for some non-criminals would allow quicker deportation of serious criminals. The indefinite stay will not give illegal immigrants a path to legal permanent residency, but will let them apply for a work permit.