By a vote of 56 to 44, Democrats were able to sustain a filibuster of a defense spending bill that would increase revenues by granting leases for oil and gas exploration in ANWR. It takes a 60-vote supermajority to end a filibuster.

The language was inserted into the defense spending bill by Republican Senator Ted Stevens of Alaska, and the powerful chairman of the Senate Appropriations Committee.

Senate Democrats who oppose opening ANWR to drilling were enraged by the tactic and vowed to defeat the measure.

Two Republicans, Senators Lincoln Chafee of Rhode Island and Mike DeWine of Ohio, sided with the Democrats.

President George W. Bush's administration has insisted that opening the area to exploration would help reduce US dependence on imported oil at a time when crude prices have spiked dramatically.

The American Petroleum Institute expressed disappointment over the action.

"The US Senate rejected an opportunity to join the House of Representatives in taking a significant step toward helping assure America's energy and economic future, which would enhance US national security," the organization representing the US oil industry said.

"ANWR's development, coupled with other American oil and natural gas supplies, greater energy efficiency, conservation and diversification, would have a far-reaching, positive impact on US consumers. That hope is now dashed by the Senate's actions."

Environmentalists, however, have argued that drilling in ANWR would yield relatively little oil and would permanently despoil the pristine nature refuge.

The environmental activist group Earthjustice called the Senate action "a hard-won environmental victory."

"Today's vote means the Arctic Refuge will remain a spectacular, unique haven for wildlife," said Sarah Wilhoite, legislative associate for Earthjustice. "Americans have made it clear that they want the Refuge protected, and today the Senate clearly heard them."

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