Maryland Gov. Martin O' Malley gives testimony to House delegates to encourage them to pass legislation to toughen gun ownership laws in the state in Annapolis on March 1. (Marvin Joseph/The Washington Post)

With Maryland’s strict new gun-control law set to take effect Tuesday, Randy Mattoon was among a crush of customers who came early Monday to Pasadena Pawn and Gun, where a sign outside advertised it was the “last day” to buy many assault rifles.

“I need something to protect my house, so I thought I’d better get it now,” said Mattoon, a 53-year-old steam fitter, as he surveyed a display case of handguns. “It ain’t cheap, but I need to take care of my family.”

Monday was the last day Marylanders could purchase handguns without being subject to new fingerprinting and training requirements. The new law, championed by Gov. Martin O’Malley (D) in the wake of the Newtown, Conn., shootings in December, also bans 45 types of assault rifles and magazines that hold more than 10 rounds and includes steps intended to make it harder for those who are mentally ill to obtain firearms.

Maryland’s response to Newtown — which has prompted an unprecedented run on gun purchases in recent months — is one of more than 300 new laws that take effect Tuesday.

Another measure passed by the General Assembly this year will allow police to pull over motorists who are talking on a hand-held mobile phone. Currently that is only a secondary offense, meaning drivers can’t be cited unless committing another violation.

Other new laws that go on the books Tuesday will ban capital punishment, make cyberbullying a crime and require all passengers in a car, including those in the back seat, to wear seat belts.

Debate over the gun law has continued long after O’Malley signed the bill into law in May. On Tuesday, gun rights advocates will make a last-ditch attempt to convince a federal judge that parts of the law violate the Constitution and should be put on hold.

As of Monday, the Maryland State Police reported receiving more than 106,000 gun-purchase applications this year submitted before the new law takes effect. That’s up from 70,099 for all of last year and 46,339 the year before.

“We’ve never in our history seen this amount of firearm purchases,” said police spokesman Greg Shipley, whose agency has struggled to keep up with the required background checks. As of Monday, there was a backlog of about 50,000 applications still waiting to be processed from applicants who won’t be subject to the new law’s fingerprinting and training provisions.

“It’s crazy. People have been lined up around my building here,” said Frank Loane, owner of the gun shop in Pasadena where Mattoon was browsing Monday morning.

Inside the store — about a 20-minute drive from the State House in Annapolis — a half-dozen employees made sales pitches and filled out paperwork as customers continued to file in.

Even some of the law’s strongest backers acknowledge that the spike in gun sales has run counter to their goal of reducing the prospect of gun violence.

“It’s unfortunate,” said Sen. Brian E. Frosh (D-Montgomery), chairman of the Judicial Proceedings Committee. “I think people have been scared into feeling they have to buy guns now, and having another 100,000 guns in Maryland is not necessarily a good thing. But ultimately the law will make people safer.”

Frosh, who shepherded the bill through the Senate, successfully added a measure to O’Malley’s legislation that gives state police more authority to inspect gun shops’ inventory.

Sen. Nancy C. Jacobs (R-Harford), who was on the opposite side of the legislative debate this year, called Maryland’s new law “a liberal, knee-jerk reaction.”

“None of this is going to keep guns out of the hands of criminals,” Jacobs said. “All it’s doing is making it harder for law-abiding citizens to exercise their Second Amendment rights. They’re making people jump through so many hoops and deal with so many delays.”

The motion for a temporary restraining order that will be heard Tuesday stems from a lawsuit in U.S. District Court in Baltimore that contends that citizens are allowed under the Second Amendment to own military-style assault rifles and magazines that hold more than 10 rounds. The plaintiffs include citizens, gun dealers and pro-gun organizations.

A brief filed by the state on Monday questions why the plaintiffs waited more than four months after the bill was signed to file suit and takes issue with numerous contentions.

“The plaintiffs’ claim that individuals using firearms for home defense are likely to need to fire more than 10 rounds at a time because they are likely to be panicked and miss with most of their shots — and thus hit things or people other than intruders at whom they are aiming — hardly supports an argument for a constitutional right,” says the brief, prepared by lawyers in the Attorney General’s Office.

Vincent DeMarco, president of Marylanders to Prevent Gun Violence, called the lawsuit “completely ludicrous” and said he is heartened that it does not take issue with the fingerprinting provisions, which he called “the most important part of the law.”

That measure is intended to prevent so-called “straw purchases” — where someone buys a gun on behalf of someone else who would not be able to pass a background check. Five other states — Connecticut, Hawaii, Massachusetts, New Jersey and New York — have similar laws.

DeMarco said Maryland’s law would be even more effective if surrounding states would adopt similar fingerprinting provisions. That would make it harder for weapons to come into Maryland illegally across state lines, he said.

A second lawsuit that has been filed in recent days raises questions about whether the state police will be able to process handgun applications under the new law in a timely manner.

A spokeswoman for O’Malley said the governor welcomed the arrival of the new law.

“The vast majority of Marylanders support these common-sense efforts to reduce gun violence,” spokeswoman Samantha Kappalman said. “It will make families safer.”