Updated

During a naturalization ceremony for 24 members of the U.S. military, President Obama plunged into the Arizona immigration controversy, warning the Justice Department would investigate civil rights violations that might arise from a new law empowering local police to check a person's legal status.

"Our failure to act responsibly at the federal level will only open the door to irresponsibility by others," President Obama said Friday at the ceremony. "And that includes, for example, the recent efforts in Arizona, which threatened to undermine basic notions of fairness that we cherish as Americans."

Top officials said Justice Department lawyers will monitor whether legal residents in Arizona are caught up in immigration raids or are in any way forced to prove their legal residency.

Critics call the new law institutionalized racial profiling.

"With just reasonable suspicion, anybody can be stopped and can be asked for papers," Angela Kelly of the liberal-leaning Center of American Progress told Fox News. "This is going to be a shot that's heard around the country."

Supporters call it a primal scream of frustration over Washington's failure to control the border. Substituting, for example, a so-called virtual fence for a real one.

"We learned that virtual fence does not work," said Sen. Jeff Sessions, R-Ala. "We've spent, I think, nearly a billion dollars for very little benefit. And I hear what they're saying now in Arizona is they want a real fence which is what has not been completed."

In an exclusive interview, Homeland Secretary Janet Napolitano, who as governor in Arizona rejected similar attempts to inspect legal status, said border security is improving.

"The numbers indeed show the border itself is more under control than it has ever been. Are we at zero? No. But have we deployed resources in …. smart and strategic way to get those numbers down? Absolutely."

The president said Congress must beef up border security, tighten workplace screening of illegals and allow millions of illegals here now a chance to earn legal residency or other states will mimic Arizona's tough new immigration law.

"If we continue to fail to act at a federal level, we will continue to see misguided efforts opening up around the country," he said.

But Republicans who beat back former President Bush's attempts at immigration overhaul say Congress and the country are more hostile to the concept that ever before.

"Right now, we need to be thinking about how to create American jobs," Sessions said. "People are out of work."