A new city law that makes it easier for victims of gun violence to sue manufacturers and dealers is in jeopardy of being superseded by federal legislation expected to be signed soon by President Bush.

The city law gives victims legal grounds to sue dealers who sell more than one handgun to the same person within 30 days and to those who fail to conduct background checks at gun shows if the weapons end up killing or injuring someone in the city.

On Thursday, however, roughly six months after the city law was enacted and before any victim had come forward to use it, Congress gave final approval to a bill that shields manufacturers and dealers from liability lawsuits.

Although the federal action was expected, it has city leaders and gun control proponents assessing the possible damage and considering the legal arguments that could be used to defend the local legislation.

Council Member David Yassky, the lead sponsor of the local law, said last night that the “federal statute raises a real threat of invalidating the city law.”

Mr. Yassky said the city could wage a successful legal argument to defend its law, but that he expected the gun lobby to argue the opposite. The legal director of the Brady Center to Prevent Gun Violence, Dennis Henigan, said there might be language in the federal statute that exempts the city from having to follow it. The city could also tweak its law to further inoculate it or introduce a new law that uses monetary penalties as an alternative to legal action, he said.

Last week, after the bill cleared its final hurdle in Congress, Mr. Bloomberg issued a statement calling the bill “a disgraceful piece of legislation that will give gun manufacturers immunity from acting negligently.”

Opponents of the city measure have long said the city did not have the authority to implement its law anyway.

A spokesman for the National Rifle Association, Andrew Arulanandam, said yesterday that the federal law was

“very narrowly worded” and that it does not protect dealers and manufacturers that sell faulty products.

“I think New York City and other municipalities would be better served if they would focus efforts on trying to curb violent crimes rather than on trying to play politics,” he said.

The city’s top lawyer, Michael Cardozo, has said that the city will continue pursuing a lawsuit that it initiated long before the local law was passed. The pending suit claims that gun manufacturers and dealers pose a threat to city residents.

Yesterday, a top attorney in the Law Department, Eric Proshansky, said the federal law was unconstitutional. He said that while local laws are generally nullified by federal laws that contradict them, they stay on the books until a victim comes forward. But most agree that the federal law would deter victims and their attorneys from expending resources to invoke the city law.