David Winston, a Republican pollster who advises the Senate Republican leadership, called the rebate an intuitive way to show voters that Republicans were on their side. "It is like putting the American family budget ahead of oil company profits," Mr. Winston said. "How do you help the American families out? Well, give them some money."

Aides for several Republican senators reported a surge of calls and e-mail messages from constituents ridiculing the rebate as a paltry and transparent effort to pander to voters before the midterm elections in November.

"The conservatives think it is socialist bunk, and the liberals think it is conservative trickery," said Don Stewart, a spokesman for Senator John Cornyn, Republican of Texas, pointing out that the criticism was coming from across the ideological spectrum.

Angry constituents have asked, "Do you think we are prostitutes? Do you think you can buy us?" said another Republican senator's aide, who was granted anonymity to openly discuss the feedback because the senator had supported the plan.