Updated

Lawmakers took the first step Thursday on a bipartisan global warming bill that would impose mandatory cuts in greenhouse gases from power plants, industrial facilities and transportation.

Sen. Joe Lieberman, I-Conn., pushed the legislation out of his global warming subcommittee by a 4-3 vote, agreeing to a number of changes aimed primarily at garnering the needed majority to advance it.

The bill calls for setting limits on carbon dioxide and other greenhouse gases that are emitted from power plants, refineries, factories and motor fuels. Polluters could exceed the limits by buying credits from companies whose emissions are under their allowable ceiling.

Lieberman called the vote "potentially a landmark event, the moment at which the United States finally began a serious fight against the threat of unchecked global warming."

Approval of the bipartisan legislation, whose co-sponsor is Sen. John Warner, R-Va., had been expected, but not without some early horse-trading for votes.

Sen. Frank Lautenberg, D-N.J., who favors more aggressive cuts in greenhouse gases, agreed to support the bill after additional emission reductions from natural gas use were included. Earlier, Sen. Max Baucus, D-Mont., was persuaded to support the measure when changes were made in the bill to help farmers.

Voting against the bill were Sens. John Barrasso, R-Wyo., Johnny Isakson, R-Ga., and Bernard Sanders, I-Vt.

The full Senate Environment and Public Works Committee plans to take up the bill in coming weeks, when its chairman, Sen. Barbara Boxer, D-Calif., is expected to seek greater greenhouse gas cuts.

Some Republicans complain the emission requirements may already be too stringent, especially in earlier years when carbon dioxide, the leading greenhouse gas, would have to be cut by at least 15 percent by 2020.

Sen. George Voinovich, R-Ohio, said earlier this week the bill will have trouble getting the 60 votes need to overcome an expected filibuster on the Senate floor unless there is an easing of the early-year requirements.

Many environmental groups support the legislation, but some environmentalists argue that it gives too much of a break to coal-burning power plants, a major source of carbon dioxide.