Two US senators announced they will unveil long-stalled legislation Wednesday to battle climate change, spurred on by a White House clarion call that "now more than ever is the time to act."

The measure, which would establish the first US nationwide plan to fight global warming, faces an uphill battle to win passage with November elections looming and aftershocks from a massive oil spill in the Gulf of Mexico.

Democratic Senator John Kerry and Independent Senator Joe Lieberman said Friday they would press ahead with the bill without their former partner in talks to cobble together a compromise bill, Republican Senator Lindsey Graham.

"We look forward to rolling-out the legislation next Wednesday and passing the legislation with the support of Senator Graham and other Republicans, Democrats and Independents this year," said Kerry and Lieberman.

President Barack Obama believes "now more than ever is the time to act," his spokesman Robert Gibbs said, noting those who support the bill "don't want to see the great progress that has been made walked away from."

The House of Representatives approved its version of the legislation, but progress in the Senate has been unsteady despite months of talks and periodic calls to action from Obama.

Hours before Kerry and Lieberman's announcement, Graham again signaled his skepticism and warned that a feud over immigration policy and the gushing oil catastrophe had swamped chances for approval this year and called for a "pause."

"We should move forward in a reasoned, thoughtful manner and in a political climate which gives us the best chance at success. Regrettably, in my view, this has become impossible in the current environment," he said.

The senator warned the legislation was doomed amid growing Democratic opposition to offshore drilling after the blast that sent the Deepwater Horizon rig to the bottom of the Gulf of Mexico and a black tide of oil into its waters.

"When it comes to getting 60 votes for legislation that includes additional oil and gas drilling with revenue sharing, the climb has gotten steeper because of the oil spill," said Graham. "There are not nearly 60 votes today."

Kerry and Lieberman, who did not refer directly to the catastrophe, said they were confident they would secure the 60 votes needed to ensure passage and overcome any parliamentary delaying tactics.

"We are more encouraged today that we can secure the necessary votes to pass this legislation this year," they said.

"The last weeks have given everyone with a stake in this issue a heightened understanding that as a nation, we can no longer wait to solve this problem which threatens our economy, our security and our environment."

Kerry recently said the bill would put the onus on polluters to curb their emissions of carbon dioxide, which scientists blame for global warming, and would provide savings to consumers on their monthly energy bills.

But the Massachusetts Democrat has hinted he may hold off on a so-called "cap-and-trade" system, under which companies would be required to curb emissions and could trade credits, giving them an economic incentive to go green.

Cap-and-trade -- the core of Europe's efforts to fight global warming -- was part of a climate package approved nearly a year ago by the House of Representatives.

Republicans have gone on the attack against cap-and-trade, branding it as a tax ahead of mid-term elections expected to be difficult for the Democrats.

In a bid to secure Republican and industry support, Kerry and Obama have voiced support for expanding nuclear power and oil drilling off the coasts of the United States.

But Obama had launched a review of offshore drilling -- already deeply unpopular with environmentalists -- after the major oil leak from the BP-leased rig near Louisiana.

Kerry, Lieberman and Graham said last year their bill would aim to cut US emissions by 17 percent by 2020 from 2005 levels, in line with the House bill and Obama's promises in international negotiations.

But the cuts would be well below promises by the European Union and Japan, which use 1990 as their base year for cuts.

Graham withdrew last month from talks with Kerry and Lieberman, citing Democratic plans to move forward on legislation to overhaul US immigration policy and accusing Obama's allies of rushing on that front purely for political gain in the elections.