ST. ANDREWS, Scotland  The United States and Britain voiced disagreement Saturday over a proposal that would impose a new tax on financial transactions to support future bank rescues.

Prime Minister Gordon Brown of Britain, leading a meeting here of finance ministers from the Group of 20 rich and developing countries, said such a tax on banks should be considered as a way to take the burden off taxpayers during periods of financial crisis. His comments pre-empted the International Monetary Fund, which is set to present a range of options next spring to ensure financial stability.

But the proposal was met with little enthusiasm by the United States Treasury secretary, Timothy F. Geithner, who told Sky News in an interview that he would not support a tax on everyday financial transactions. Later he seemed to soften his position, saying it would be up to the I.M.F. to present a range of possible measures.

“We want to make sure that we don’t put the taxpayer in a position of having to absorb the costs of a crisis in the future,” Mr. Geithner said after the Sky News interview. “I’m sure the I.M.F. will come up with some proposals.”