A proposed 30 percent minimum tax on millionaires backed by President Barack Obama - dubbed the Buffett tax after investor Warren Buffett who supports it - would raise about $47 billion over a decade, according to a congressional report.

The Joint Committee on Taxation, a nonpartisan body that estimates tax changes for lawmakers, on Tuesday updated an earlier report forecasting that the tax would raise $31 billion over the period, citing economic modeling errors.

Either way, the revenue is far less than the $1 trillion or more that would be lost from scrapping the alternative minimum tax. The AMT also is meant to be a minimum tax on the wealthy. Democrats have said the Buffett tax could replace the AMT.

The Buffett tax proposal has little chance of passing with Republicans in charge of the House of Representatives and its prospects in the Democratic-controlled U.S. Senate are murky.

Taxes are a major topic on the campaign trail ahead of Obama's re-election bid this November.

(Reporting by Kim Dixon; Editing by Kevin Drawbaugh and Bill Trott)

Barack obama Warren buffett