WASHINGTON - Potential presidential rivals John McCain and Barack Obama are joining with Sen. Joe Lieberman on a plan they say would reduce global-warming gases by two-thirds over the next four decades.

Their bill, to be announced today, is intended to cut the heat-trapping emissions by 2 percent a year through midcentury.

It is considered sure to produce a contentious debate on climate control in the new Democratic-run Congress and draw strong opposition from the White House and industry.

Sens. McCain (R., Ariz.), Obama (D., Ill.) and Lieberman (D., Conn.) are calling for mandatory caps on greenhouse emissions for power plants, industry and oil refineries.

Their plan would require releases of heat-trapping gases to return to 2004 levels by 2012 and to 1990 levels by 2020.

Carbon dioxide, produced from the burning of fossil fuels, is the primary greenhouse gas.