A federal judge is forbidding the city from calling Mayor Bloomberg as a witness in its landmark suit against a gun salesman from Georgia.

At a hearing yesterday, the judge, Jack Weinstein of U.S. District Court in Brooklyn, explained his decision to keep the mayor off the witness stand by saying, “I’m not going to turn the case into a media circus for either side,” according to a partial transcript.

A jury will be picked next week to hear the city’s claim that a store owned by the gun dealer, Jay Wallace, sold a disproportionate number of the guns that have been recovered in crimes committed in New York City. Mr. Wallace’s store, Adventure Outdoors, is one of 27 out-of-state gun dealers sued by the city, and the first of three expected to go to trail. The suits have been a central part of Mr. Bloomberg’s anti-gun campaign.

The city had intended to call Mr. Bloomberg as a witness to discuss gun violence in the city. Judge Weinstein suggested that lower-ranking city officials could testify about that.

“From the city’s point of view, he doesn’t add a thing to your case,” Judge Weinstein said, before turning to an analogy.

“If we were trying a Guantanamo incarceration, I certainly wouldn’t allow anybody to call the president in,” Judge Weinstein said. “We’d have the people in charge of Guantanamo and their superiors.”

It is unclear whether a deposition the mayor provided for the case will be offered as evidence at trial.