Donald Trump is far ahead of the Republican field on Long Island and Hillary Clinton holds a commanding lead in the Democratic contest, according to a Newsday/News 12/Siena College survey of Nassau and Suffolk county voters.

And in a potential head-to-head matchup, Long Islanders give Trump a 3 percentage point edge over Clinton — though former New York Mayor Michael Bloomberg would top both in a three-way contest.

Trump has a 37-point lead over his closest Republican rivals, Ohio Gov. John Kasich and Sen. Marco Rubio (R-Fla.), according to the poll released Thursday.

The brash businessman received support from 49 percent of Republicans surveyed, compared with 12 percent each for Kasich and Rubio. Sen. Ted Cruz (R-Texas), so far the only Republican to defeat Trump in a caucus or primary, received 8 percent.

Among Democrats, Clinton, the former secretary of state, New York senator and first lady, leads Sen. Bernie Sanders of Vermont, 51 percent to 33 percent.

If the general election were to pit Trump against Clinton, Long Islanders favor Trump 41-38 percent — which is within the poll’s margin of error of plus or minus 3.1 percentage points. In a theoretical three-way contest, Bloomberg — taking votes from both parties — gets 35 percent, Trump 29 and Clinton 26.

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The poll of 984 registered voters on Long Island was conducted Feb. 14-18 and 21-22.

That Trump is leading the GOP in New York isn’t a big surprise. That he’s leading by such a wide margin is, said pollster Don Levy, director of the Siena College Research Institute.

“That’s an enormous lead, ” Levy said. “Barring some incredible events, it’s hard to envision Trump not winning New York.”

New York holds its primary on April 19. By that time, the GOP field — now at five candidates — could be down to two or three.

Long Islanders said the most important single issue in making their decision in the presidential race is jobs and the economy, chosen by 37 percent of respondents. The threat posed by ISIS was next at 24 percent and health care was third at 15 percent.

Trump leads by a wide margin in every demographic breakdown: age, education level, income level, religion and political viewpoint. He received 49 percent from those who called themselves conservative Republicans. The next closest was Rubio, with 16.

Trump “speaks his mind. He’s different. He’s not a typical politician,” said Republican Greg Dalma, 53, of East Islip. Dalma, who owns a medical business, believes Trump’s business background makes him better suited to bring back American jobs from China and other nations, and he supports Trump’s call for a wall along the Mexican border.

Dalma called the rest of the GOP field “typical politicians who are full of it.”

Republican Jerry Pascale, 58, a retired Massapequa carpenter, said he backs Cruz because “he’s the only strict constitutionalist” in the GOP field.

“No one likes him, and I see that as a good thing that no one likes him,” Pascale said. “The GOP elite, the establishment, want to hold onto the power they have. But Cruz is for term limits and reforming government and sometimes that makes you unpopular.”

Clinton, who served as a New York senator from 2001 to 2009, has a big lead over Sanders despite 27 percent of Democrats saying they have an unfavorable view of her. “In a head-to-head matchup, they come back to her,” Levy said.

Clinton leads Sanders by 25 percentage points in Nassau (54-29), but just 10 in Suffolk (48-38). She leads 55-36 among those Democrats describing themselves as “liberal.”

Christine Barnett, a 31-year-old Freeport Democrat, said Sanders is making too many “unrealistic” promises.

“Tuition-free college . . . that’s not even realistic,” Barnett said, also knocking Sanders’ proposal for single-payer health care. “He’s getting people on his side by saying these things. But they’re not realistic.”

In contrast, Ian Rawley, a 22-year-old Hofstra University student, backs Sanders because “Clinton has a little too much baggage.” He cited her vote for invading Iraq in 2003 and her acceptance of speaking fees from large financial institutions.

“Sanders talks a lot about issues others aren’t raising,” Rowley said, citing minimum wage and income inequality.

If the presidential contest came down to Trump versus Clinton, Long Islanders give a slight edge to Trump. That’s in part because independent voters favor Trump 39-30.

Hersh Mehta, 23, a Hicksville software developer, said he’s an independent who considers himself liberal but would support Trump over Clinton.

“”The problem I have with Hillary, I basically have a trust issue with her,” Mehta said. “ . . . With Benghazi, the email servers, all of that, I don’t see that as being presidential or trustworthy.”

In contrast, Republican Regina Conner would cross party lines to support Clinton in part because she believes Trump isn’t qualified. She said she’s upset about “these things he says on TV, about Mexicans and other people.”

“I don’t think he would be a good president,” Conner, 49, of Rockville Centre, said. She said she agrees with most of Clinton’s stances and added “it would be good to see a woman president.”

Bloomberg, who is said to be considering running as an independent, “has the best favorability numbers in the entire poll,” Levy said. In the Long Island poll, Bloomberg takes votes from Republicans and Democrats in almost equal proportions.

“I think that exposes a weakness on the part of both Hillary and Trump,” Levy said.

With Laura Figueroa