HARRISBURG — Pennsylvania Attorney General Kathleen Kane is leaving it to the governor’s office to defend a lawsuit challenging a National Rifle Association-backed law that was designed to dismantle illegal municipal firearms ordinances, officials said Friday.

A spokesman for Gov. Tom Corbett said the governor’s legal office will defend the law against the challenge led by Philadelphia, Pittsburgh and Lancaster.

Corbett, a Republican who opposes new forms of gun control, signed the law last month. The law widens the ability of the NRA or gun owners to successfully sue over municipal firearms ordinances.

“We can find no legitimate reason for the attorney general to decline to defend the commonwealth in this case,” said Corbett’s spokesman, Jay Pagni.

The law takes effect in the coming weeks, and opponents fear it will unleash a wave of expensive lawsuits against dozens of cities and towns that have sought to curb gun violence but bumped up against a Legislature that has resisted new gun control measures.

However, Corbett leaves office Jan. 20 after losing last month’s election, and he will be replaced by Democrat Tom Wolf, who opposes the law.