WASHINGTON — Republicans on a key US Senate committee were absent Tuesday as debate opened on a Democratic proposal for sweeping climate change legislation.

The Senate Environment and Public Works Committee opened its critical debate on the plan at 9:00 am (1400 GMT) without its Republican members, despite last-ditch efforts to avert an opposition boycott from Democratic Senator Barbara Boxer, who chairs the committee.

Republican Senator George Voinovich did show up soon after the meeting opened, but only to deliver a statement opposing the measure.

Supporters of the climate change legislation are pushing hard to pass it ahead of December's make-or-break global summit in Denmark.

In a statement, the Republicans said they would oppose the bill until they had a "comprehensive analysis" of the economic impact of the legislation from the federal watchdog agency, the US Environmental Protection Agency (EPA).

"There are five weeks until the Copenhagen meetings begin, which, according to the EPA administrator, leaves enough time for chairman Boxer to work with us and the EPA to conduct a full economic analysis" of the legislation, the Republican statement read.

In his statement, Voinovich said that the committee "lacks a full analysis" of the measure, so considering the bill "seems a little premature."

He said that he and his Republican colleagues "need time to read the bill and prepare amendments".

Boxer however said that the committee "released the EPA analysis and there is no reason at all to do additional analysis.

"The only reason is to delay" the process, she said. "We must move forward."

Boxer emphasized that committee was "not rushing... We have a full blown analysis backed up by 340,000 pages."

Republican committee members were absent because they were unhappy with the EPA analysis, she said.

"We have taken every step to welcome them at our table. If we all care about jobs we need to work on this bill together," Boxer said.

Boxer also said that Senate Majority Leader Harry Reid has committed to carry out "a full analysis when the final bill is put together."

The US House bill calls for cutting US greenhouse gas emissions by 17 percent from 2005 levels by 2020 and by 83 percent by 2050. The Senate's slightly more ambitious bill calls for a 20-percent cut by 2020.

Both bills would create a cap-and-trade regime, the government would set the total level of domestic emissions allowable and then allocate quotas to companies.

Firms that emit less than their quota would be allowed to sell their surplus allocation to others that exceed theirs. Those in excess could also face fines.

The Senate text -- which is likely to change considerably before a final vote -- also makes a push for nuclear energy research and training, and promotes natural gas as a clean energy source.

Democratic Senator John Kerry, a co-author of the bill, has warned that US leadership is on the line ahead of the global climate change talks in Denmark's capital Copenhagen next month.

The December 7-18 summit is aimed at a treaty that will tackle carbon emissions and their impacts, and encourage a switch to cleaner energy after 2012, when the current Kyoto Protocol pledges expire.

Kerry has said the full Senate will not vote on a final bill before the Copenhagen summit.