(CBS/AP) 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. 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. That guidance also covered those potentially subject to a legislative proposal, known as the DREAM Act, 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 States, 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. "As a matter of law, they are eligible for a work authorization card, basically a taxpayer ID card, but that decision is made separately and on a case-by-case basis," said the official, who spoke on the condition of anonymity because he was not authorized to discussed the change publicly. The official said the change will give authorities the chance to keep some cases from even reaching the court system. The message to agents in the field, the official said, would be "you do not need to put everyone you come across in the system." If an immigrant whose case has been stayed commits a crime or other circumstances change, their case could be reopened. Sen. Dick Durbin, D-Ill., a longtime supporter of immigration overhaul and the DREAM Act, applauded the policy change. "These students are the future doctors, lawyers, teachers and, maybe, senators, who will make America stronger," Durbin said in an emailed statement. "We need to be doing all we can to keep these talented, dedicated, American students here, not wasting increasingly precious resources sending them away to countries they barely remember." According to White House officials, the policy could also benefit illegal immigrants who have family members in the States -- among them partners of gay, lesbian and bisexual people, The New York Times reported. Richard Socarides, an attorney and former adviser on gay issues to President Clinton, told the Times: "The new policy will end, at least for now, the deportations of gay people legally married to their same-sex American citizen partners, and it may extend to other people in same-sex partnerships." Do you approve of this more lenient approach to illegal immigrants by the Obama administration? Rep. Michael McCaul, R-Texas, said the Obama administration was implementing reforms "against the will of Congress and the majority of American people we represent." "It is just the latest attempt by this president to bypass the intended legislative process when he does not get his way," McCaul said in a statement. "The fact that we have a backlog and prioritize deportations is nothing new. This policy goes a step further granting illegal immigrants a fast-track to gaining a work permit where they will now unfairly compete with more than 9 percent of Americans who are still looking for jobs." Other Republicans have previously criticized the DREAM Act and other immigration legislation that would provide a path to legal status as amnesty. Following Morton's June memo, Rep. Lamar Smith, R-Texas, introduced a bill to block the administration's use of prosecutorial discretion and called the use of that discretion "backdoor amnesty."