The administration had wanted to attend the April 20-25 meeting in Geneva, although it warned in late February that it would not go unless significant changes were made to the draft text.
Some revisions - including the removal of specific critical references to Israel and problematic passages about the defamation of religion - were negotiated.
But the State Department said the text retains troubling elements that suggest support for restrictions on free speech and an affirmation of the findings of the first World Conference Against Racism, held in Durban, South Africa, in 2001 that the U.S cannot endorse.
"Unfortunately, it now seems certain these remaining concerns will not be addressed in the document to be adopted by the conference next week," State Department spokesman Robert Wood said in a statement. "Therefore, with regret, the United States will not join the review conference."
Concern is high that the meeting may descend into heated debate over Israel that marred the last such gathering eight years ago, especially since Iran's hardline president - who has called for Israel's destruction - will attend.
The Durban meeting was dominated by quarrels over the Middle East and the legacy of slavery.
The United States, under the Bush administration, and Israel walked out over attempts to liken Zionism - the movement to establish a Jewish state in the Holy Land - to racism. The reference was later dropped, but concerns about anti-Semitism remained in the final text.
Plans to reaffirm the 2001 document were of particular concern to the Obama administration.
"(It) singles out one particular conflict and prejudges key issues that can only be resolved in negotiations between the Israelis and Palestinians," Wood said.
Planning for the upcoming meeting, which is to review progress made in fighting racism since Durban, has been underway for months and was shunned by the Bush administration.
But once Obama took office, his team decided to engage in the process as part of its broader aim of reaching out to the international community.
After sending delegates to a preparatory meeting, the administration announced on Feb. 27 that it would not participate in further planning talks or the conference itself unless the changes were made.
In the weeks that followed, the U.S. pressed its European allies to lobby for an acceptable text and officials had held out hope until earlier this week that the negotiations would produce an acceptable document.
Possible participation by Washington remained on the table, pending the changes, even after it was learned that Iran's hardline President Mahmoud Ahmadinejad - who has called for the destruction of Israel - would go.
Pro-Israel groups in the United States vehemently opposed U.S. participation while human rights advocates and organizations like TransAfrica and members of the Congressional Black Caucus thought it was important to attend.
Just hours before Saturday's announcement, Human Rights Watch appealed for the U.S. to go, saying it "should stand with the victims of racism."
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On the Net:
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