WASHINGTON – In a shocking blast at Barack Obama that was caught on tape, the Rev. Jesse Jackson said, “I wanna cut his nuts out.”

He made the astonishingly vulgar remark as he accused the presumptive Democratic presidential nominee of giving moral lectures to African-Americans.

“See, Barack [has] been talking down to black people . . . I wanna cut his nuts out,” Jackson said.

His whispered comments – accompanied by his hand-miming a cutting motion – were picked up by a live mike before an interview on health care in Fox News Channel’s Chicago studio Sunday.

In an effort to blunt the controversy, Jackson apologized publicly at a news conference before the tape aired last night on Bill O’Reilly’s “The Factor” show on Fox News Channel.

“It was not a public speech or a declaration,” Jackson said at the news conference, although he admitted his language was “regretfully crude” and “hurtful.

“For any harm or hurt that this hot-mike conversation may have caused, I apologize,” Jackson said earlier in a statement.

Jackson told The Associated Press he couldn’t recall everything he’d said, but couched the remarks as part of a discussion about Obama speaking to black churchgoers.

In such settings, Obama has urged greater emphasis on fatherhood, and most recently told students to stick with school and forget about careers as rap stars or pro basketball players.

Jackson said on the “Fox & Friends” mike that Obama was hurting his relationship with black voters, “that the senator was cutting off his you-know-whats with the black people and black churches.”

Jackson told CNN he called the Obama campaign to apologize, and reiterated his support.

“My support for Senator Obama’s campaign is wide, deep and unequivocal,” he said. “I cherish this redemptive and historical moment.”

O’Reilly said last night he had chosen not to air comments that would have been even more damaging to Jackson.

Obama’s spokesman Bill Burton said Obama “of course accepts Reverend Jackson’s apology.”

But the Rev. Al Sharpton admonished Jackson and cautioned against dividing black voters.

Obama “is running for president of all Americans, not just African-Americans,” he said. We “must be careful not to segregate Senator Obama and impose some litmus test that is unfair and unproductive.”

Even Jesse Jackson Jr., an Obama supporter and congressman from Chicago, condemned his dad’s remarks. “I’m deeply outraged and disappointed in Reverend Jackson’s reckless statements about Senator Barack Obama,” he said.

churt@nypost.com