Bernie Sanders has pulled to within 10 points of Hillary Clinton among New York voters, according to a new poll Wednesday — slashing her lead from 21 points just a month ago in the same survey.

Clinton leads, 52 percent to 42 percent, among likely Democratic voters in the Siena College poll, compared with the 55-34 advantage she had on March 7.

Siena pollster Steve Greenberg said Sanders had made enormous strides among voters under 35 and now commands 76 percent of their support.

“The younger voters are feeling the ‘Bern,’ but the question is: Will they come out and vote in large numbers, as older voters historically do?” Greenberg noted.

Experts debated whether the surge is too little, too late for Sanders heading into Tuesday’s New York primary.

“If he can keep it close, low single digits, that’s momentum for him,” Monmouth College polling director Patrick Murray told The Post.

But Larry Levy, a political analyst at Hofstra University, said “The Bern” may be flaming out.

“There are no symbolic victories left for Bernie Sanders. He has to get delegates. He can’t afford symbolic victories, and it’s not going to get any easier because of the demographics,” Levy said.

Meanwhile, more than 15,000 people attended a Sanders rally in Washington Square Park on Wednesday night.

Earlier, he and Clinton traded boasts of important new labor endorsements.

The city’s transit workers union endorsed Sanders during a rally at union headquarters in downtown Brooklyn.

“We all know in this room that you don’t have a great and growing middle class unless you have a great and growing union movement. Unions are the last line of defense against a corporate agenda,” Sanders said.

He later addressed striking Verizon workers represented by the Communications Workers of America, which also has endorsed him.

“This is about a company that wants to take health care benefits away from its workers. These workers are standing up against injustice, and I stand with them,” the Vermont socialist declared.

Verizon CEO Lowell McAdam posted a response, saying Sanders’ comments were “disconnected from reality.”

After Sanders finished speaking to the transit workers, Clinton crowed that the electrical workers union had lined up behind her.

“If we want to get serious about raising incomes, we have to get serious about supporting union workers,” she said, ticking off her support for a higher minimum wage, paid family leave and federal spending to create jobs.

“I will never stop fighting for the American worker.”

Clinton later appeared at a rally at the Midtown headquarters of SEIU Local 1199, which represents health care workers and is working to help elect her president.