Steve Schwarzman, billionaire head of buyout giant The Blackstone Group, shockingly likened President Obama’s threat to impose higher taxes on private equity firms to Adolf Hitler’s invasion of Poland.

“It’s a war,” declared Schwarzman, speaking at a private board meeting of a nonprofit organization. “It’s like when Hitler invaded Poland in 1939.”

Schwarzman’s over-the-top comments reportedly stunned those in attendance.

Yesterday, Schwarzman said he was sorry about his choice of words, but he wasn’t backing away from the issue.

“I apologize for what was an inappropriate analogy,” he said.

“However, the fundamental issue of the administration’s need to work productively with business for the benefit of the overall economy is still of very serious concern, not only to me, but also to large parts of the business community,” he told The Post.

Schwarzman’s “Hitler” comments, first reported by Newsweek, come as the industry’s largest lobbying group, the Private Equity Council, requests its members to wage a “grassroots” campaign against the tax hikes.

It is asking some of the largest private-equity bosses to urge executives to confront their local representatives about the planned tax changes.

The “grassroots” campaign was first reported by The Post.

Billionaire Schwarzman is furious over looming plans on Capitol Hill to jack up taxes that private-equity firms generate from buying and selling companies. Known as “carried interest,” those profits are currently taxed at 15 percent, but could be dialed up to a 35 percent tax rate — a move that could strip private equity of billions in cash.

Sources said that Schwarzman feels as though Obama has taken a tough stance against Wall Street firms, contributing to an us-vs.-them mentality. At the same time, Obama is taking campaign contributions from some of the same firms that he has been vilifying.

Known for being outspoken, Schwarzman is no complete stranger to verbal gaffes.

He also ignited a controversy last year, when he made another World War II reference. At that time, he compared the subprime mortgage crisis to Nagasaki, Japan, after the United States dropped an atomic bomb on the city. He said the bomb left the city “with noodle salesmen with few noodles or customers.”

Obama’s dustup with one of the leaders of the private equity sector comes just a few weeks after GE Chief Executive Jeff Immelt launched his own verbal salvos against the president.

“Business [does] not like the US president, and the president did not like business,” Immelt said during a dinner meeting with Italian business heads in Rome.

mark.decambre@nypost.com

