Jeff Gadell believes his older brother — an NYPD officer killed in the line of duty — is his guardian angel and watches over other cops, too.

“He’s been on my shoulder for 30 years,” Gadell, 47, of Wantagh, said Wednesday of his idol — killed in a June 1986 shootout outside a Far Rockaway, Queens, rooming house. “And I hope that he’ll be there for another 30 years.”

On the street bearing the fallen officer’s name, the Gadell family, top NYPD officials, and retired and current officers honored Scott Gadell at his Far Rockaway precinct stationhouse on the 30th anniversary of his death.

The 22-year-old U.S. Army Reserve veteran was fatally shot after just 11 months on the job.

“Scott was a hero for the way he lived and for what he helped accomplish,” Chief of Department James P. O’Neill said. “He believed good should prevail over evil, and he worked to make it so.”

Scott Gadell was scheduled to work the night of June 28, 1986, but he switched to a day shift so he could attend his brother’s Wantagh High School graduation the next day.

While on patrol, Gadell and his partner searched for a man who had fired at two men. The officers saw the suspect — later identified as Errol Campbell of Brooklyn — run into the rooming house.

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The officers gave chase and a shootout soon ensued. Campbell shot Gadell in the head as the young officer paused to reload his revolver.

Campbell, who would be charged and convicted of murder, was sentenced to 25 years to life and is still behind bars.

The tragedy prompted the NYPD to equip officers with speedloaders — devices that enabled them to load all six rounds in their .38-caliber revolvers in one motion. Officers were later issued 9-mm. semi-automatic handguns.

On Wednesday, NYPD officials rededicated a plaque bearing Gadell’s badge number — 27037 — that has hung in the lobby of the 101st Precinctstationhouse, where Gadell worked.

Retired NYPD Sgt. Wilton Sekzer, 71, then president of the Shomrim Society, a religious and fraternal organization of Jewish NYPD members, recalled his reaction when he learned Gadell had been killed.

“You could’ve knocked me over with a feather,” Sekzer said of Gadell, who took part in the society’s events. “I loved that kid.”

Through the years, the Gadell family has comforted other grieving relatives of fallen officers — repaying the kindness they felt.

It means a lot to the family that his brother is not forgotten, said Jeff Gadell, a Nassau public works employee.

Scott’s name lives on in two of his nephews: Ryan Scott Gadell, 4, and Cole Scott Gadell, 9.

Jeff Gadell said his son Ryan sometimes wears his uncle’s police cap at home — and proudly calls him a “hero.”