A fourth mayor has withdrawn from Mayor Bloomberg’s coalition against illegal guns, officials said.

Mayor Mary Wolf of Williamsport, Pa., said in an interview yesterday that she withdrew from Mayors Against Illegal Guns because she thought it was attempting to erode all gun ownership, not just illegal guns.

Mr. Bloomberg and Mayor Menino of Boston formed the coalition last year to lobby for laws that would prevent guns from illegally ending up in the wrong hands.

In a letter to Mr. Bloomberg, Ms. Wolf wrote, “I have learned that the coalition may be working on issues which conflict with legal gun ownership, and that some actions on your behalf are dubious.”

Some of those actions, she said, include the city’s civil lawsuits against gun dealers in five states whom private investigators videotaped making illegal “straw sales.”

The other mayors who have left the coalition are Jared Furhriman of Idaho Falls, Idaho, Mark Begich of Anchorage, Alaska, and Kevin Jackson of Rio Rancho, N.M.

A spokesman for Mr. Bloomberg, Jason Post, said in a statement that the gun lobby was distorting the facts about the coalition.

“All mayors in this coalition share a common concern about illegal guns and a common desire to move beyond the tired old politics of exaggeration and mischaracterization that has unfortunately dominated the illegal gun debate in the past,” he said.

The owner of a firing range and gun dealership in Williamsport, Frank Tripoli, said he learned more about the coalition’s activities through the National Shooting Sports Foundation, a trade group representing 3,600 retailers, distributors, manufacturers, publications, and other organizations.

“We live in a community that is a hunting, fishing, and shooting sports-focused group of people,” he said. “I think a lot of people wrote to the mayor.”