New York ? A fortresslike metal door guards the entrance to writer Pete Hamill’s Tribeca home. The door opens to a drab, industrial foyer where an equally unpromising elevator chugs up to the author’s floor.

There, everything brightens.

Waiting in an open door is Hamill, 67, trim and relaxed. His silvering hair is cut short, his face a complex map of laugh lines. His voice is gravelly, the result of a recent brush with bronchitis. He leads a visitor into a warm and quiet apartment. The walls are cluttered with paintings, hefty art books and Mexican masks, each face carved into a colorful rictus.

In a way, Hamill’s apartment mirrors the homes he created for Cormac O’Connor, protagonist of Hamill’s new novel about immortality, “Forever.” O’Connor’s first home, in mid 18th-century Ireland, is a “house built like a fortress,” its walls 2 feet thick. His last, in the 21st century, is a duplex on Duane Street in downtown Manhattan. It is filled with books, paintings and African masks.

But Cormac and Hamill have more in common than apartments. Both are newspapermen, both Irish, both paint and both have sworn off alcohol — Hamill, after an addiction he searingly documented in his memoir, “A Drinking Life.”

“In certain ways,” says Hamill, “the things Cormac does are extensions of the boy I was in my teens and 20s, wanting to be 18 things at once. He gets to do all of these things.”

Hamill first imagined a novel based around an immortal character when he turned 60 and realized he wouldn’t have time to try all the things that interested him.

The story centers on Cormac who, shortly after traveling to New York to avenge his father’s death, is granted eternal life by an African priestess, so long as he remains in Manhattan.

Though Hamill, who calls immortality a curse, says he would hate to be Cormac, this conceit does enable him to “watch” the city grow from a wilderness port to the city that never sleeps. Hamill explores several periods of the island’s history, including the 1830s and the reign of the notorious politician Boss Tweed, whom the author depicts in a far more favorable light than many historians have.

“I wanted to write about these periods to get closer to them,” says Hamill, “to touch them and feel them and smell them.”

Hamill was born and raised in Brooklyn to parents who immigrated here from Belfast, Northern Ireland. After leaving school at 16, he went to work as a sheet metal worker in the Brooklyn Navy Yard and then joined the Navy, where he finished high school. Following a yearlong stint at Mexico City College in 1956, he returned to New York.

In 1960, Hamill took a job at the New York Post where he grew as a reporter and editor. He has served as editor-in-chief at both the Post and New York Daily News.

“Forever” is not, as author and fellow Daily News columnist Michael Daly points out, the “cliche New York novel — hyper real and street smart.”

As with his previous novel, “Snow in August,” Hamill wanted to take “Forever” beyond the journalistic novel. Heavily infused with doses of African and Celtic mythology, the book moves fluidly between historical fact and fantasy.

Hamill chose to emphasize the city’s African roots because he believes they have so often been overlooked. He likens New York to an alloy, “with all of these various metals, including the African contributions, forging something that was stronger than any one of them alone.

“If you come, and you’re tough enough — which means that you have to absorb slights and injuries and the stupidities of idiots — if you believe that work and education will open the treasure house of America, then everything is yours. It’s been won for you,” he says.

New York, he says, “shown for more than a hundred years the possibilities of this American vision, which says that there’s a place for everybody.”