Legal analysts expect the city to be able to proceed with civil lawsuits against 15 gun dealers targeted by Mayor Bloomberg’s out-of-state sting operations, despite the Department of Justice’s decision yesterday not to file criminal charges against them.

The city had given the evidence to the Bureau of Alcohol, Tobacco, Firearms, and Explosives to examine for potential criminal charges. But in a letter sent to the city on Tuesday, the director of the executive office of United States Attorneys, Michael Battle, said its offices “concluded that the circumstances surrounding the purchases do not rise to a level that would support a criminal prosecution.”

Healso warned the mayor’s office of “potential legal liabilities” in using a private investigation firm to “undertake actions typically reserved for law enforcement agents.”

The letter was first reported in the New York Daily News yesterday.

Mr. Bloomberg’s criminal justice coordinator, John Feinblatt, said in an interview that the city never wanted to prosecute the dealers criminally.

“This has no bearing on our civil cases,” he said. “Our goal was to make dealers play by the rules, not to put them in jail, not to drive them out of business.”

The civil lawsuits were filed last year as part of the mayor’s campaign to reduce the number of illegal guns entering New York City. Fifteen dealers were targeted in the first round of lawsuits; an additional 12 lawsuits were announced in December.

So far, seven of 27 dealers targeted by the sting operations conducted by a white-collar investigation firm, James Mintz Group, have settled with the city. They have agreed to give a city-appointed monitor complete access to the stores for three years.

The sting operations simulated “straw purchases,” in which one person buys a gun that is really for someone else, according to the mayor’s office.

A law professor at Albany Law School, Timothy Lytton, said the lack of criminal charges did not necessarily hurt a civil lawsuit’s chances for success. The threshold for a criminal charge is higher than that for a civil case.

“More what it shows is there is a continuing lack of zeal by the federal government to investigate and enforce these laws at a dealer level,” he said. “New York has taken it upon itself to enforce federal laws by suing for this kind of nuisance in the face of the federal government, who has decided not to enforce these laws.”

The president of the Citizens Crime Commission, Richard Aborn, said: “The goal of the lawsuits is to stop these dealers engaging in straw purchases. … You want to send the message that the sale you’re making could result in a lawsuit.”

A New York lawyer representing eight of the dealers in the two rounds of lawsuits, John Renzulli, had a different interpretation.

“They intend to use these illegal operations as a major point in their case,” he said. “I think it has a bearing on the case.”

The out-of-state lawsuits are one part of Mr. Bloomberg’s threepronged approach to reducing the number of illegal guns in New York. He has increased NYPD enforcement and lobbied Congress for stricter laws.

The lawsuits have riled several pro gun rights groups, including the Second Amendment Foundation and the National Shooting Sports Foundation, which have called on the Justice Departmen to prosecute the private investigators for breaking federal firearm laws. A law enforcement source said the department has declined to pursue charges against the private investigators.