* Waxman bill would cut emissions faster than Obama's plan

* Would require 1/4 of electricity from renewables by 2025

* Many Republicans likely to oppose Democratic bill (Adds details throughout and byline)

By Richard Cowan

WASHINGTON, March 30 (Reuters) - The chairman of a key committee in the U.S. House of Representatives will propose climate change legislation that would cut greenhouse gas emissions at a rate that is somewhat more aggressive than proposals by President Barack Obama, sources said on Monday.

The legislation by House Energy and Commerce Committee Chairman Henry Waxman would require that U.S. carbon emissions be reduced by 20 percent from 2005 levels by the year 2020, 42 percent by 2030 and 83 percent by 2050, according to House Democratic aides who asked not to be identified.

The U.S. "cap and trade" emission control regime would not begin to take effect until 2012, when a 3 percent reduction from 2005 levels would be required, the aides said.

Obama has asked Congress for legislation that would bring reductions of around 15 percent by 2020 and over 80 percent by 2050. Waxman is set to unveil his draft legislation on Tuesday.

Under its cap and trade plan, the Obama administration has proposed raising $646 billion by selling permits to power plants, oil refineries and other industrial facilities that would limit the greenhouse gases they could emit. Some of the money would go back to consumers to help them pay for higher energy costs, as well as supporting alternative energy initiatives.