The US Senate has voted to allow a plan that opens up a remote wildlife refuge in the northern state of Alaska to oil drilling.
Much of Alaska is currently a wilderness
Senators voted 51-49 against an amendment which would have struck the measure from the federal budget.
The plan has long been a key part of President Bush's energy plan, as a means to reduce US reliance on imports.
Democrats and some Republicans have opposed the plan, arguing that the wilderness should be left untouched.
The 19-million-acre (7.7-million-hectare) Alaska Arctic National Wildlife Refuge, known as America's Serengeti, is home to caribou, migratory birds and other wildlife.
It has been specifically protected by Congress from development.
No longer promising
New Mexico Republican Pete Domenici said before the vote that the refuge had the country's "most significant onshore production capacity".
"We should do everything we can to produce as much as we can," he said, quoted by the Associated Press news agency.
ARCTIC NATIONAL WILDLIFE REFUGE
Area: 19 million acres, the size of North Carolina
Home to 45 types of mammal, including polar bear and caribou, and 180 species of bird
Oil potential: Up to 16 billion barrels
But Massachusetts Senator John Kerry, who proposed the amendment, said there was no way the US could drill its way out of its energy crisis.
Correspondents say there is not much interest among the oil companies in drilling in the refuge, as its economic potential no longer seems promising.
However, some Republicans see the plan as a political manoeuvre which could open the way for other environmentally controversial projects such as drilling off Florida or California.
Previous votes to remove the ban on drilling have failed, but the Senate's Republican majority increased after last year's elections.
Democrats had tried to block the plan with a filibuster, but majority leaders put the provision into a budget document immune to these tactics.
Opponents of the plan were then forced to seek an amendment stripping the mention of drilling from the budget, but fell short of the required 51 votes in the 100-seat chamber.
The Senate is due to vote on the budget later in the week, and its wording still needs to be approved by the House of Representatives.