WASHINGTON, October 27, 2009 (AFP) - President Barack Obama's Senate allies launched a major push Tuesday to pass legislation to fight climate change, arguing US leadership was "on the line" ahead of a global summit in December.

"World leaders are waiting for a signal that we are serious before they make commitments" at the talks in Denmark's capital Copenhagen, said Democratic Senator John Kerry. "America's leadership is significantly on the line here."

Kerry, the legislation's lead author, was the first witness as the Senate Environment and Public Works Committee opened three days of hearings with time for action running short for Washington to act before the international forum.

The House of Representatives passed a White House-backed bill in June to create a "cap and trade" regime to regulate emissions of greenhouse gases blamed for global warming.

The full Senate is not expected to act on its version of the legislation before the talks in Denmark, but the measure could have cleared the committee, which is led by Democratic Senator Barbara Boxer.

Obama, showing during a trip to Florida that he will not wait for lawmakers to act, was to unveil the largest-ever upgrade of the US electricity grid, in a $3.4-billion bid to unleash a new era of renewable energy consumption.

Some 100 firms, manufacturers, utilities and cities will get awards worth from 400,000 to 200 million dollars to help build a nationwide "smart energy grid" to cut costs and improve reliability of the creaking system.

In Washington, Obama's secretaries of energy, interior and transportation, as well as his Environmental Protection Agency chief, urged senators to act quickly, warning US "clean energy" firms had lost ground to overseas rivals.

"When the gun sounded on the clean energy race, the United States stumbled. But I remain confident that we can make up the ground," said Energy Secretary Steven Chu.

Obama has said he wants to make as much progress as possible to reassure skeptics at the Copenhagen UN conference that the United States is pressing ahead with aggressive climate change remedies.

Obama's Republican foes and some uneasy Democrats oppose the White House strategy, with some warning it would inflict severe economic pain on traditional industries that might not survive the transition to cleaner energy.

"The bill is no doubt ambitious, but it's also extremely costly," Republican Senator Jim Inhofe, a longtime climate change doubter, said as the hearing began, disputing an Environmental Protection Agency study that found it would cost most US families no more than 30 cents per day.

"Our bill is the best way to proceed," said Boxer.

"It provides flexibility to businesses and powerful incentives to drive innovation. It helps consumers, workers, agriculture, transportation, energy efficiency, wildlife, cities, counties, and it will launch an economic transformation," she said.

The US House of Representatives approved a so-called "cap and trade" emissions regime in June, and the Senate is now poised to take up the measure with a new poll showing nearly six in 10 Americans support such a plan.

Under the expected 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 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.

The Senate text also makes a push for nuclear energy research and training, and promotes natural gas as a clean energy source.

About sixty percent of respondents to a CNN/Opinion Research Corporation survey said they favor such an approach, while 37 percent said they oppose it. The survey's error margin was plus or minus three percentage points.