WASHINGTON — Former Senator Bob Dole of Kansas sat slightly slumped in his wheelchair on the Senate floor on Tuesday, staring intently as Senator John Kerry 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 Mr. 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 while seated at their desks, out of respect for Mr. Dole, 89, a Republican who was the majority leader.

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

A majority of Republicans who voted against the treaty, which was modeled on the Americans With Disabilities Act, said they feared that it would infringe on American sovereignty.