WASHINGTON — Former Sen. Bob Dole of Kansas sat slightly slumped in his wheelchair on the Senate floor on Tuesday, staring toward Sen. John Kerry as he gave his most impassioned speech all year, in defense of a United Nations treaty that would ban discrimination against people with disabilities.

Senators from both parties went to greet Dole, leaning in to hear his wispy reply, as he sat in support of the treaty, which would require that people with disabilities have the same general rights as those without disabilities. Several members took the unusual step of voting aye from their desks, out of respect for Dole, 89, a Republican who was the majority leader.

Then, after Dole’s wife, Elizabeth, rolled him off the floor, Republicans quietly voted down the treaty that the ailing Dole, recently released from Walter Reed National Military Medical Center, so longed to see passed.

Among GOP fears about the disabilities convention were that it would codify standards enumerated in the U.N. Convention on the Rights of the Child — and therefore U.N. bureaucrats would be empowered to make decisions about the needs of disabled children — and that it could trump state laws concerning people with disabilities. Proponents of the bill said these concerns were unfounded.

The measure — modeled on the Americans With Disabilities Act — required two-thirds support for approval. It failed 61 to 38. Idaho’s Mike Crapo and Jim Risch, both Republicans, voted against it.

Kerry, D-Mass., his voice rising as senator after senator moved slowly into the chamber, rejected the concerns of Republicans and made a moral argument for approval of the treaty.

Dole, he said, had not come to the Senate floor “to advocate for the United Nations.”

“He is here because he wants to know that other countries will come to treat the disabled as we do,” he added.

Approval of the treaty, Kerry said, would demonstrate that “what we do here in the United States Senate matters.” He added, “Don’t let Sen. Bob Dole down.”

A handful of Republican senators voted for the measure, notably Sen. John McCain of Arizona, in opposition to the other Arizona Republican senator, Jon Kyl; so did Sens. Kelly Ayotte of New Hampshire, John Barrasso of Wyoming, Scott P. Brown of Massachusetts, Susan Collins and Olympia Snowe of Maine, Richard G. Lugar of Indiana and Lisa Murkowski of Alaska.

Sen. Jerry Moran of Kansas originally praised the treaty in a news release with McCain in May but then voted against it. Sen. Thad Cochran of Mississippi voted yes at the beginning of the roll call vote, and switched his vote to no. Calls to both senators’ offices were not returned.

Sen. Harry Reid of Nevada, the majority leader, said the measure would return to the Senate floor in the 113th Congress.

“It is a sad day when we cannot pass a treaty that simply brings the world up to the American standard for protecting people with disabilities because the Republican Party is in thrall to extremists and ideologues,” he said in a statement.