AFTER 50 years in Al bany, Staten Island state Sen. John Marchi is calling it quits, bringing to a close the nation’s longest state legislative career.

Marchi, who turns 85 next month, will forever be remembered for the critical role he played in reshaping New York politics – and making conservatives a force to be reckoned with.

In 1969, he was an obscure legislator with a reputation for blandness (who called himself “the Perry Como of politics”) as well as integrity and diligence. Yet that year he was tapped by outer-borough conservatives to challenge the city’s liberal mayor, John Lindsay, in a Republican primary.

It looked like an uphill fight. Liberals like Nelson Rockefeller, Jacob Javits and Lindsay held firm control of the local party. But conservatives (who’d formed their own party a few years earlier to push the GOP rightward) knew that they reflected the Republican base. Indeed, New York Republicans were heavily middle-class Catholics – the group most alienated by Lindsay, a Manhattan liberal who openly disdained communities like Bay Ridge and Canarsie.

And so Marchi, though under-funded and lacking any campaign organization, proceeded to knock Lindsay off in the primary. The final numbers were relatively close – but only because Lindsay did so well in Manhattan. Marchi took the other four boroughs with 62 percent of the vote.

Had the Democrats nominated a left-wing candidate, Marchi might have had a shot in November. But the surprise winner of that primary was law-and-order candidate Mario Procaccino. With the conservative vote split and leftist Democrats fearful of a Procaccino mayoralty, Lindsay – who piously denounced Marchi’s win as a victory for “hatred, fear and negativism” – emerged as the favorite, running on the Liberal line.

Marchi wasn’t a dynamic candidate. His speeches were cerebral, and he wasn’t comfortable with glad-handing and street campaigning. But he sounded a theme ahead of its time: As Vincent Cannato notes in “The Ungovernable City,” Marchi appealed to “the forgotten New Yorker” – the “decent, law-abiding citizen who recognizes his responsibility to his neighbors, his fellow citizens and his community. Yet because he isn’t part of a special interest or pressure group, he has been ignored and forgotten by the professional politicians and playboy politicians at City Hall.”

In the debates, Marchi emerged as the class of the field. Even liberal Pete Hamill (then a Post columnist) acknowledged that Marchi refused to pander and “does not accuse voters of bad faith if they disagree with his political ideas.” On the contrary, wrote Hamill, “he has spoken intelligently about most issues.”

In the end, Marchi finished a distant third, with just 23 percent. Many conservatives had defected to Procaccino as the stronger anti-Lindsay candidate.

But Marchi proved where the GOP base lay – and that conservatives could win votes by appealing to the middle class. The next year, a New York conservative did just that: James Buckley, running on the Conservative Party line, went to Washington by asking those voters, “Isn’t it time we had a senator?”

It was the precursor of a political revolution that would go national in 1980 when Ronald Reagan became president. But it was John Marchi’s mayoral run that sounded the initial charge.

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A POSTSCRIPT: Sami Merhi, the New Jersey Democrat disendorsed from his party’s ticket for the Passaic County Board of Freeholders because of remarks he made in 2002 that seemed to imply support for Palestinian terrorism, got in touch after deadline for last week’s column.

Though insisting he abhorred “all violence and terrorism by all groups,” he at first refused to condemn Hamas and Islamic Jihad by name. He insisted that if he began criticizing other specific organizations, he’d “then be asked about groups in Afghanistan and Pakistan and so on and it would never stop.”

Then I pointed out that others have played rhetorical games by saying that Hamas engages in legitimate resistance – and that Israeli settlers and soldiers are not “innocent victims.” Bottom line: When he condemns “all groups engaged in terrorism,” does he include Hamas and Islamic Jihad suicide bombers?

“Yes,” he replied, “Hamas, Islamic Jihad, all of them.”

Does he share the belief that some Israeli lives are not innocent?

“No,” said Merhi, whose 25-year-old godson was killed on 9/11. “Anyone who loses a life to terrorism, including suicide bombing, is innocent.”

Merhi wants to know why he never heard from Gov. Jon Corzine and Sen. Bob Menendez before they muscled the Passaic County Dems into dropping him. Fair enough. But if only he’d been that clear and unambiguous all along, he would have spared himself a lot of grief.