Gov. Andrew M. Cuomo defended a New York State law that has made it easier to take guns away from people who have been deemed mentally unstable, saying on Sunday that the number of people banned from owning firearms since the law took effect over 18 months ago could be too low.

Speaking after a campaign rally in the Bronx, two weeks before the election, Mr. Cuomo was reacting to a report in The New York Times on Sunday, which disclosed that 34,500 people in New York have been reported to a state database as a danger to themselves or others, and prohibited from owning firearms for five years.

Some supporters for the mentally ill have said the number seemed high, and suggested that the law may have included people who were not truly dangerous, stigmatizing the mentally ill.

Mr. Cuomo said that compared to the roughly 140,000 people in the state hospitalized for mental illness in a year, 34,500 seemed to be a conservative number. “I’ve heard concerns that the number is too low, because obviously there are about 110,000 people who are institutionalized, but yet could still get a gun,” Mr. Cuomo said.