In a move that will once again thrust him into the national spotlight, Mayor Bloomberg filed a lawsuit against 15 gun dealers yesterday, accusing them of negligence for allowing their weapons to end up in the hands of criminals.

The lawsuit stems from a six-week undercover operation, in which investigators working for the city used hidden cameras to videotape transactions with sales clerks at out-of-state gun stores.

The suit names gun stores in five states – Georgia, Ohio, Pennsylvania, Virginia, and South Carolina – that the city claims sold guns to customers knowing they would turn the weapons over to criminals. It asks the court to stop illegal sales by placing monitors in stores to ensure compliance with federal law. It also asks for compensatory and punitive damages.

“These dealers are the worst of the worst,” Mr. Bloomberg said to reporters before playing two of the videos on a flat-screen television at City Hall. The videos show teams of two people shopping for guns in what is commonly known as “straw purchasing.” One person asks detailed questions about the weapon and then the other actually fills out the paperwork.

Over the past three months Mr. Bloomberg has intensified his campaign to eradicate illegal guns. He has testified in front of a congressional committee against legislation that would restrict data sharing on guns, and hosted mayors from across the country to talk about cracking down on firearms.

But this suit, which was filed in federal court in Brooklyn, is the most significant action the mayor has taken since the start of his second term. Mr. Bloomberg criticized the Bureau of Alcohol, Tobacco and Firearms, the agency charged with enforcing federal gun laws, saying it would be an “understatement” to say they are “asleep at the switch.”

Officials at the Nation Rifle Association said they are against straw purchases, but had not reviewed the suit.

Mr. Bloomberg – joined by the city’s police commissioner, Raymond Kelly, and its chief lawyer, Michael Cardozo – buttressed his case with statistics. He said more than 300 New Yorkers were murdered with illegal handguns last year.

The 78-page suit is studded with examples of transactions at the 15 stores and of crimes committed with illegal guns, including the fatal shooting of 2 1/2-year-old David Pacheco Jr. who was hit by a stray bullet in the Bronx on Easter Sunday.

The mayor said that because more than 80% of guns recovered at city crime scenes come from other states, “our efforts to stop this bloodshed have to reach across state lines.”

Experts who have studied guns had mixed views on the latest lawsuit. A separate suit that the city filed against gun manufacturers in 2000 had a boomerang effect, prompting Congress to shield gun makers from civil liability.

A law professor at George Mason University, Michael Krauss, predicted that the new suit would be dismissed, calling it “even more frivolous than the other suit.”

“The question is: What gives Mayor Bloomberg the right to sue?” he said.

The head of the Second Amendment Research Center at Ohio State University, Saul Cornell, predicted a more successful outcome.

“The problem with the earlier suit is that there was a perception they were trying to shut down the gun industry,” he said. “This suit … targets people who are breaking the law.”

The owner of Mickalis Pawn Shop in Summerville, S.C., which has been named in the suit, said he has received “clean slates” from the federal authorities and that Mr. Bloomberg should be going after criminals in his own city.

“I don’t see how a small pawn shop in South Carolina has any influence over gun violence in New York,” Larry Mickalis said. “What he’s saying is that I’m involved in some sort of inner-city gun ring in New York and that’s just not true.”

Mr. Bloomberg is scheduled to meet today in Washington, D.C., with several lawmakers, and said he planned to talk more about guns.