ANNAPOLIS, Md. - Gov. Martin O'Malley signed a gun-control measure on Thursday to give Maryland some of the nation's tightest gun laws, and the National Rifle Association plans to challenge it in court.Part of the law requires people to submit fingerprints to the state police to get a license to buy a handgun."States with similar licensing provisions have substantially lower gun death rates than states that do not, so if we want better results we have to make better choices, and this legislation is part of that series of the better choices that we are making," O'Malley said.The other states include New Jersey, New York, Massachusetts, Connecticut and Hawaii.O'Malley, a Democrat, proposed the bill in January in response to the December shooting in Newtown, Conn., where a gunman killed 20 children and six adults.Opponents are backing the NRA's plans to file a lawsuit. Delegate Neil Parrott of Washington County has led petition drives to put legislation on the ballot for voters to decide in recent years. He has announced he supports court action rather than trying to overturn the law in a referendum."The National Rifle Association's position and concerns will be made very clear when we file our lawsuit," Jacqueline Otto, an NRA spokeswoman, said in an email.Meanwhile, Marylanders to Prevent Gun Violence plan to launch a campaign to highlight the effectiveness of the law, which takes effect Oct. 1. The group is set to air television ads Monday."The ads will reinforce the fact that this law will save lives," said Vincent DeMarco, the president of the group.The measure bans 45 types of assault weapons, but people who own them now will be able to keep them. Gun magazines will be limited to 10 bullets. It also bans gun ownership by people who have been involuntarily committed to a mental health facility.In addition, Maryland State Police will be able to suspend the licenses of gun dealers who fail to comply with new record-keeping obligations. The provision will allow the state police to supplement enforcement efforts of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives. The measure also requires mandatory reporting to law enforcement of lost or stolen firearms.Earlier this month, Attorney General Doug Gansler released a 25-page legal review expressing confidence the law is constitutional and legally defensible.The O'Malley administration also highlighted what the measure does not do. For example, it does not require additional licensing procedures for hunting rifles and shotguns. It also doesn't require companies who manufacture assault weapons in Maryland to stop production. The measure also does not require current lawful gun owners to retroactively obtain a license.