The US Senate on Thursday was to take up a fiercely worded resolution formally apologizing for the "fundamental injustice, cruelty, brutality, and inhumanity of slavery" of African-Americans.
The move came five months after Barack Obama became the first black US president, and on the eve of the June 19 "Juneteenth" celebration of the emancipation of African-Americans at the end of the US Civil War in 1865.
If approved by the Senate, the measure would go to the House of Representatives, where a similar resolution passed by voice vote in July 2008, only to wither in the upper chamber.
The bill, which does not require Obama's signature, states that the US Congress "acknowledges the fundamental injustice, cruelty, brutality, and inhumanity of slavery and Jim Crow laws" that enshrined racial segregation at the state and local level in the United States well into the 1960s.
The Congress also "apologizes to African-Americans on behalf of the people of the United States, for the wrongs committed against them and their ancestors who suffered under slavery and Jim Crow laws."
And it "expresses its recommitment to the principle that all people are created equal and endowed with inalienable rights to life, liberty, and the pursuit of happiness, and calls on all people of the United States to work toward eliminating racial prejudices, injustices, and discrimination from our society."
The measure takes pains, however, not to fuel the push for the US government to pay reparations to the descendants of African slaves.
"Nothing in this resolution (a) authorizes or supports any claim against the United States; or (b) serves as a settlement of any claim against the United States," it says.
The United States has never offered a formal apology for the chattel slavery of Africans, though former president Bill Clinton expressed regret for the practice during a March 1998 trip to Africa.
His successor, George W Bush, called slavery "one of the greatest crimes of history" during a July 2003 visit to Goree Island, Senegal, a former slave-trade port.
Some US states have officially adopted resolutions expressing regret or remorse for slavery.
"An apology for centuries of brutal dehumanization and injustices cannot erase the past," said the Senate resolution, which was introduced by Democratic Senator Tom Harkin.
"But confession of the wrongs committed and a formal apology to African-Americans will help bind the wounds of the Nation that are rooted in slavery and can speed racial healing and reconciliation," it said.
The Senate was expected to decide the measure by voice vote, meaning that there would be no record of how individual lawmakers voted.
The debate came as the United States marked the 80th anniversary of civil rights icon Martin Luther King, Jr's birthday, the 200th anniversary of the birth of Abraham Lincoln, who formally declared blacks in secessionist states free during the civil war in 1863.
And 2009 is also the hundredth year since the founding of the National Association for the Advancement of Colored People (NAACP) civil rights group.