Law-enforcement agencies, including the NYPD, should boycott gun manufacturers who produce high-capacity magazines like the one used to shoot Rep. Gabrielle Giffords and 19 others, a top city official said yesterday.

“If Glock will not stop selling these magazines to consumers, then the New York City Police Department should start buying the firearms they need from a different company,” Public Advocate Bill de Blasio said.

“The New York Post editorial board has rightly argued that the Glock-manufactured 30-round magazines, like the one used by clearly disturbed Jared Loughner, present an unacceptable risk to human life, and at the same time no justifiable civilian purpose.”

The issue came to light after Loughner, 22, killed six people, including a federal judge and 9-year-old girl, in a fusillade of bullets Saturday in Tucson, Ariz., with his legally purchased Glock and 33-round magazine.

His brutal assault, which left Giffords and 13 others hospitalized, was stopped only when he was tackled after pausing to reload.

The Post’s editorial board yesterday demanded the NYPD use its substantial purchasing power to influence gun companies to stop selling the high-capacity magazines to civilians.

Bridgeport, Conn., Mayor Bill Finch, a member of Mayor Bloomberg’s Mayors Against Illegal Guns Coalition, told The Post a boycott is “an excellent idea.”

“To me, these are weapons of mass destruction. You have guns that can fire off a large number of rounds almost instantly up against the police, who have popguns in comparison,” said Finch, a Democrat.

He added that Joe Gaudette, chief of Bridgeport’s 410-officer police department, would not make any future firearms purchases from companies that make the extended magazines, including two Connecticut-based manufacturers, Sturm Ruger and Colt.

The NYPD, however, said a boycott wouldn’t work.

“Were the department to boycott manufacturers based on their sale and marketing of high-capacity magazines, there would be no source of reliable weapons for any newly hired officers going forward, making a federal ban the practical solution,” said spokesman Deputy Commissioner Paul Browne.

In 2010, the NYPD spent $656,599 on 1,337 weapons for new recruits, with $283,292 to Smith & Wesson, $215,280 to Glock, and $157,927 to Sig Sauer.

None of the gun manufacturers responded to requests for comment, but an industry spokesman said, “We will not participate in politicizing this tragedy.”

Nationally, the private handgun market generates about $800 million in sales a year, according to Rommel Dionisio, a vice president at Wedbush Securities who tracks firearm manufacturers.

By comparison, he estimated law-enforcement sales totaled $80 million to $90 million a year, with Glock, a private Austrian company, commanding about two-thirds of the market.

Meanwhile on Capitol Hill, Rep. Carolyn McCarthy (D-Nassau) circulated legislation to ban sales of magazines that hold more than 10 bullets.

Her legislation, with a companion bill sponsored by Sen. Frank Lautenberg (D-NJ) in the Senate, closes a loophole that allowed the high-capacity magazines despite their ban in six states, including New York and New Jersey.

Between 1994 and 2004, the magazines were illegal under the Federal Assault Rifle Ban, but those made prior to the assault were grandfathered in, making prosecution of offenders difficult.

(Source: NY Post)