TRENTON, Aug. 22 — The New Jersey attorney general, Anne Milgram, on Wednesday ordered local law enforcement agencies to inquire about the immigration status of criminal suspects and notify federal authorities whenever they believe someone arrested is in the country illegally.

The directive comes amid growing debate across the state over the role of local officials in immigration questions since the Aug. 4 schoolyard slayings of three friends in Newark. One of the prime suspects in the murders, Jose Lachira Carranza, is an illegal immigrant from Peru who was out on bail despite three prior felony arrests, in part because the authorities never checked his immigration status.

“There’s a need that was brought home to us all recently with the tragic events in Newark for a uniform state policy,” Ms. Milgram, the state’s top law enforcement officer, said at a news conference here, promising random compliance checks to ensure that local officials are following the policy, effective immediately.

A spokesman for Immigration and Customs Enforcement, the federal agency, praised the new policy Wednesday, saying, “We welcome this newly expanded cooperation throughout the State of New Jersey.”

Ms. Milgram has talked often about helping local law enforcement officials deal with illegal immigrants in a manner that promotes public safety without treading on human rights. That has become more precarious for politicians since the shooting.

On the one hand, Mayor Cory A. Booker of Newark has repeatedly said that he opposes the notion of involving city police in immigration matters, and Paula T. Dow, the Essex County prosecutor — whose office was one of several that did not check Mr. Carranza’s immigration status — was even more pointed, saying her policy was to notify immigration officials only upon conviction.

On the other hand, a growing chorus of officials — including the State Senate president, Richard J. Codey, a Democrat, and Assemblyman Alex DeCroce, the Republican minority leader — have recently urged the state to adopt a tougher stance. And on Monday, Representative Tom Tancredo, a Republican from Colorado who is running for president on a conservative immigration platform, accused Newark officials of being complicit in the murders because of their lax approach.

Until now, local law enforcement agencies had broad discretion — and widely divergent practices — on whether to check immigration status or report suspicious candidates to federal authorities. The Hudson County prosecutor’s office, for example, already routinely does so; the West Orange Police Department, which had arrested Mr. Carranza for assault last fall, has no set procedures for contacting the immigration service.

There has been a similar patchwork of policies around the country.

After a Kentucky judge jailed 17 Hispanic immigrants without bail last year for traffic infractions, the state’s attorney general, a Democrat, issued an advisory telling local police officers to consult a national database to check the status of people they arrest, and to report illegal immigrants to federal authorities.

When Mitt Romney, a Republican presidential candidate, was governor of Massachusetts, he signed an agreement with the federal immigration agency giving specially trained state police officers the authority to enforce immigration law. But in January, the new governor, Deval Patrick, a Democrat, rescinded the agreement and restricted the training to corrections officials charged with finding illegal immigrants convicted of crimes in the state’s jails.

There are now 26 local agencies around the country that have signed formal agreements with the federal government to deputize correctional officers to check the immigration status of prisoners.

Under Ms. Milgram’s directive, local law enforcement officials are to ask about any arrested person’s citizenship, nationality and immigration status, and notify the immigration service of anyone believed to be here illegally.

The local officers cannot, however, ask immigration questions of victims or witnesses to a crime, because, Ms. Milgram said, it is vital that the authorities retain the trust and cooperation of the public in conducting criminal investigations.

The United States attorney for New Jersey, Christopher J. Christie, who stood with Ms. Milgram at the news conference, said bluntly that racial profiling would not be tolerated and that any police officer believed to be abusing the directive would be dealt with “very, very seriously.”

Michael Wishnie, a professor at Yale Law School who has represented immigrant-rights groups, said that while the New Jersey directive appeared to be a measured response to “the politics of the moment,” it still raised concerns.

“One of the problems with police doing status inquiries even after serious offenses is it encourages people to flee,” Mr. Wishnie said, adding that it might not be easy for local officers to sort out the roles between victims, witnesses and criminals. Sometimes, he said, “You bring everyone back to the station house, and sort it out there,” he noted. “The reality of police practice is, the distinctions are often too finely drawn to protect victims and witnesses.”