In a reference to Mr Obama, Mr Jackson had said on US Fox News: "I want to cut his nuts off", not knowing his comments were picked up by a live microphone.
Mr Jackson had said he thought Mr Obama was "speaking down to black people".
The reverend said he was "very sorry for any harm" and that he had "deep and wide" support for the Obama campaign.
Mr Jackson has been a key civil rights campaigner and was unsuccessful when running for the Democratic presidential nomination in 1984.
'Moral Content'Mr Jackson was talking to a guest ahead of a live interview on Fox on Sunday in Chicago when he made the remarks.
He was discussing the question of Mr Obama's speeches on morality that the presidential candidate had made in black churches.
He said he thought there were other key issues facing the black community, such as unemployment and crime.
The reverend added: "See, Barack been, um, talking down to black people on this faith based... I want to cut his nuts off... Barack... he's talking down to black people."
Mr Jackson said he had called the Obama campaign to apologise "for any harm or hurt that this hot mic private conversation may have caused".
"My support for Senator Obama's campaign is wide, deep and unequivocal."
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http://news.bbc.co.uk/2/hi/americas/7498995.stm