Six Republicans voted with Democrats in favor of ratifying the Convention on the Rights of Persons with Disabilities, but the final vote -- 61-38 in favor -- was five votes short of the two-thirds necessary to join more than 150 other countries that have ratified the treaty.
Senate Majority Leader Harry Reid, D-Nev., said the treaty was modeled on U.S. law and he will bring it up for another vote in the next Congress.
In a statement, Reid said the U.N. treaty "simply brings the world up to the American standard for protecting people with disabilities" and said the Senate rejected it "because the Republican Party is in thrall to extremists and ideologues" and "a small group of Republican senators fear the Tea Party more than they care about equality for people with disabilities."
"Their arguments against the treaty had no basis in fact -- the treaty does not change United States law," Reid said.
In a statement late Tuesday, the White House expressed disappointment "that the overwhelming majority of Senate Republicans today blocked the Convention on the Rights of Persons with Disabilities, which would enshrine American standards that have been developed through decades of bipartisan cooperation."
The White House said it hoped the Senate will reconsider the treaty in the next Congress and noted ratification would not result in any change to U.S. law but "would position the United States to support extending across the globe the rights that Americans already enjoy at home."
"This in turn would improve the lives of Americans with disabilities -- including our wounded service members -- who wish to live, work, and travel abroad. It would also allow our businesses to operate on a more level playing field and reaffirm American leadership on disability rights."
Opponents, including Sens. James Inhofe, R-Okla., and Mike Lee, R-Utah, argued the treaty would establish new abortion rights and interfere with families' choices in the education of their children, The Hill reported.
"This unelected bureaucratic body would pass recommendations that would be forced upon the United States if we were a signatory," Inhofe said.
Supporters pointed out the treaty would not establish any new rights in U.S. courts and would be non-binding in any case.
Lee asked why the Senate should ratify the treaty if it "does nothing."
"I have not said it does nothing," Sen. John Kerry, D-Mass., said. "I said it does not change U.S. law. That is different from saying it doesn't do anything. If it didn't do anything I wouldn't be here nor would President Bush have signed it."
Kerry said the treaty would afford the United States the opportunity to advocate for rights of U.S. military veterans and citizens abroad, The Hill reported.
Republicans Kelly Ayotte of New Hampshire, John Barrasso of Wyoming, Scott Brown of Massachusetts, Susan Collins of Maine, Dick Lugar of Indiana, John McCain of Arizona and Lisa Murkowski of Alaska voted with Democrats in favor of ratification.