Gov.Andrew M. Cuomo and lawmakers agreed on Monday to a broad package of changes to gun laws that would expand the state’s ban on assault weapons and would include new measures to keep guns away from people with mental illnesses.

The state Senate, controlled by a coalition of Republicans and a handful of Democrats, approved the legislative package just after 11 p.m. by a lopsided vote of 43 to 18. The Assembly, where Democrats who have been strongly supportive of gun control have an overwhelming majority, planned to vote on the measure Tuesday.

Approval of the legislation would make New York the first state to act in response to the mass shooting at an elementary school in Newtown, Conn., last month.

Mr. Cuomo, a Democrat, had pressed lawmakers to move quickly in response to Newtown, saying, “the people of this state are crying out for help.” And the Legislature proceeded with unusual haste: Monday was the first full day of this year’s legislative session.

“We don’t need another tragedy to point out the problems in the system,” Mr. Cuomo said at a news conference.

“Enough people have lost their lives,” he added. “Let’s act.”

The expanded ban on assault weapons would broaden the definition of such weapons, banning semiautomatic pistols and rifles with detachable magazines and one military-style feature, as well as semiautomatic shotguns with one military-style feature. New Yorkers who already own such guns could keep them but would be required to register them with the state.

“The message out there is so clear after Newtown,” said the Assembly speaker, Sheldon Silver, a Democrat from Manhattan. “To basically eradicate assault weapons from our streets in New York as quickly as possible is something the people of this state want.”

In an acknowledgment that many people have suggested that part of the solution to gun violence is a better government response to mental illness, the legislation includes not only new restrictions on gun ownership, but also efforts to limit access to guns by the mentally ill.

The most significant new proposal would require mental health professionals to report to local mental health officials when they believe that patients are likely to harm themselves or others. Law enforcement would then be authorized to confiscate any firearm owned by a dangerous patient; therapists would not be sanctioned for a failure to report such patients if they acted “in good faith.”

“People who have mental health issues should not have guns,” Mr. Cuomo told reporters. “They could hurt themselves, they could hurt other people.”

But such a requirement “represents a major change in the presumption of confidentiality that has been inherent in mental health treatment,” said Dr. Paul S. Appelbaum, the director of the Division of Law, Ethics, and Psychiatry at the Columbia University College of Physicians and Surgeons, who said the Legislature should hold hearings on possible consequences of the proposal.

“The prospect of being reported to the local authorities, even if they do not have weapons, may be enough to discourage patients with suicidal or homicidal thoughts from seeking treatment or from being honest about their impulses,” he said.

The legislation would extend and expand Kendra’s Law, which empowers judges to order mentally ill patients to receive outpatient treatment.

And it would require gun owners to keep weapons inaccessible in homes where a resident has been involuntarily committed, convicted of a crime or is the subject of an order of protection.

The legislative package, which Mr. Cuomo said he believed would be “the most comprehensive package in the nation,” would ban any gun magazine that can hold over 7 rounds of ammunition — the current limit is 10 rounds. It would also require background checks of ammunition buyers and automated alerts to law enforcement of high-volume purchases.

The legislation would increase penalties for multiple crimes committed with guns, would require background checks for most private gun sales, and create a statewide gun-registration database.

Senator Jeffrey D. Klein of the Bronx, the leader of an independent faction of Democrats who have allied with the Republicans to control the Senate, said the measure met the goals of many lawmakers.

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