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.”

The Associated Press obtained a copy of the letter.

Republicans complained that the new policy circumvents Congress.

“They have created a working group that appears to have the specific purpose of overruling, on a ‘case-by-case’ basis, an immigration court’s final order of removal, or preventing that court from even issuing such an order,” House Judiciary Committee Chairman Lamar Smith, R-Texas, said in a statement. “The Obama administration should enforce immigration laws, not look for ways to ignore them. The Obama administration should not pick and choose which laws to enforce. Administration officials should remember the oath of office they took to uphold the Constitution and the laws of the land.”

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. Immigrant advocacy groups have complained that people who had not yet been convicted of a crime were being caught up in the system.

In June, the director of Immigration and Customs Enforcement, John Morton, sent a memo to agents outlining when and how they could use discretion in immigration cases.