A Georgia gun dealer that Mayor Bloomberg sued as part of his effort to get firearms off the city’s streets hit the mayor with a lawsuit of his own yesterday, saying Mr. Bloomberg slandered his business and broke federal law.

Adventure Outdoors Inc., which is being represented by a former Republican congressman of Georgia, Bob Barr, filed a $400 million lawsuit in Superior Court of Cobb County.

The business was one of 15 so-called rogue dealers in five states that Mr. Bloomberg sued two months ago after an undercover sting operation. The 13-page complaint filed yesterday said that Mr. Bloomberg and several others in his administration smeared the dealer’s reputation and that its undercover investigators lied on federal Bureau of Alcohol, Firearms, and Tobacco forms.

Observers say the legal action could be the first in a string of lawsuits against the city in connection with the mayor’s lawsuit. Many who oppose the suit charge Mr. Bloomberg with attacking the Second Amendment. He has denied doing so, stressing that he is only going after illegal guns.

Still, the new twist gives Mr. Bloomberg the chance to talk more about an issue he has carved out as one of the signatures of his second term amid speculation that he wants to run for higher office.

“Not only did Bloomberg engage in an improper and unlawful transaction, but then he and others issued public statements that we believe are slanderous and defamatory,” Mr. Barr said yesterday during a telephone interview.

The shop’s owner, Jay Wallace, said his name has been “trashed.”

“I run my business with honesty and integrity, and I take pride in being part of the firearm industry,” he said, the Associated Press reported.

Mr. Bloomberg, who is leading a national coalition of mayors to push for stronger laws against illegal guns, dismissed the suit as a “publicity stunt.”

“I’m just thrilled that he sued me,”Mr. Bloomberg said with a smile at Gracie Mansion.”We’re on the right side of this. I think we have a responsibility to uphold the laws, and a publicity stunt like that is not going to overshadow the fact that a small number of reckless gun dealers are selling guns that are committed in crimes and we have young men and women that are dying here in this city.”

He then added: “I’m just thrilled that they mentioned me by name. Hopefully they get the spelling right.”

The complaint — which also names the city’s police commissioner, Raymond Kelly;wah the mayor’s criminal justice coordinator, John Feinblatt, and the city’s chief lawyer, Michael Cardozo — invokes the Racketeer Influenced and Corrupt Organizations Act and claims that city officials conspired to deceive the store into selling the gun. The result, the suit said, was that the dealer was “maliciously” libeled and slandered.

In May, Mr. Bloomberg sued 15 businesses that he claimed sold guns to customers knowing they would hand over the weapons to other people.

The city said that between 1994 and 2001, Adventure Outdoors sold 21 guns that ended up being used in New York City crimes. Mr. Barr said the city had its information wrong.

The city’s suit relied on a six-week undercover operation in which investigators working for the city went into stores and pretended to be customers. They used hidden cameras to capture illegal “straw” purchases.

Mr.Barr also sent letters to the U.S.attorney in Atlanta, David Nahmias, and to Georgia’s state attorney general, Thurbert Baker, requesting that they investigate the city’s undercover operation.

A lawyer representing a gun dealer in Queens that was also the target of a Bloomberg sting, John Chambers, said he was not surprised that the suit was filed.

“I don’t think the city has a legal leg to stand on,” Mr. Chambers said. “I don’t know what Bloomberg’s problem is.” He said he expects more dealers to sue the city in connection with the case.

Mr. Feinblatt said the city followed the law in its investigation and that law enforcement has an obligation to act.

“The only people who broke the law here are the dealers,” Mr. Feinblatt said.

In announcing his lawsuit in May, Mr. Bloomberg called the 15 dealers targeted the “worst of the worst” and said that more than 300 New Yorkers were murdered with illegal handguns in the city last year. He also criticized the Bureau of Alcohol, Tobacco and Firearms, the agency charged with enforcing gun laws, saying its officials were “asleep at the switch.”

A spokesman at the ATF’s New York office, Joseph Green, declined to comment.