The Senate blocked opening the nation's largest untapped oil reserve in an Alaska wildlife refuge Wednesday, denying President Bush his top energy priority and delivering a victory to environmentalists who said drilling would threaten wildlife.

It was a stinging defeat for Sen. Ted Stevens, R-Alaska, one of the Senate's most powerful members, who had hoped to garner more votes by putting the measure onto a defense spending bill. That forced senators to choose between supporting the drilling measure, or risking the political fallout from voting against money for the troops and hurricane victims.

Instead, Stevens found himself a few votes shy of getting his wish.

Sen. Maria Cantwell, D-Wash., who led the floor debate in opposition to the drilling provision, called it "legislative blackmail" and said Democrats agreed they "were not going to get jammed" by the tactic.

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Republican leaders could not break a Democratic filibuster threat over the drilling issue, falling three votes short of the 60 votes need to advance the defense spending bill to a final vote. Majority Leader Bill Frist, R-Tenn., a supporter of drilling, voted with those opposing it so he would have the right to ask the Senate to reconsider the issue in a second vote later.

Hours later, however, the Senate stripped the Alaska drilling language from the defense legislation, then passed the bill and sent it to the House, which was scheduled to reconvene Thursday afternoon. The House earlier had passed the defense spending bill with the Alaska drilling provision in it.

Democrats as well as a number of Republicans were already angered by Stevens' tactic that delayed action on the $453.5 billion defense bill including $29 billion for hurricane relief, the war and border security, and $2 billion to help low-income households pay this winter's heating expenses.

"Our military is being held hostage by this issue, Arctic drilling," fumed Sen. Harry Reid, the Democratic leader.

But Stevens, 82, the Senate's most senior Republican, known for his sometimes cantankerous nature and fiery temper, expressed frustration, but had no apologies.

"Every time this subject comes up ... the minority has filibustered," Stevens complained, reminding colleagues of his 25-year campaign to get Congress to allow development of an estimated 10 billion barrels of oil beneath the coastal tundra of the Arctic National Wildlife Refuge in the far northeastern corner of his state.

After the vote, Democrats celebrated as did environmentalists, knowing they had tangled with one of the Senate's toughest members and won.

"It took a lot of guts for a lot of people to stand up," Sen. Joe Lieberman, D-Conn., said after the vote. He said he expects the 43 senators who voted against drilling — all but four Democrats as well as GOP Sens. Mike DeWine of Ohio and Lincoln Chafee of Rhode Island — not to yield to further pressures and change their vote.

But no one believes the issue — which has galvanized environmentalists determined to protect the refuge from development — is going away.

"I expect to see it again next year," said Sen. John Kerry, D-Mass., a longtime drilling opponent.

"Yes, it'll be back," agreed Lieberman.

Environmentalists rejoiced, aware that never before had drilling proponents come so close to victory. The House already had approved the defense bill with Steven's drilling measure included and President Bush was eager to sign it. Congress approved ANWR drilling in 1995 as part of a budget package that was immune from Senate filibuster, but President Clinton, a drilling opponent, vetoed it.

The Sierra Club called it "an against-all-odds" victory.

"Drilling proponents pulled out all the stops, and tried every trick in their playbook," said Sierra Club Executive Director Carl Pope. "This is a tremendous victory for all Americans and proof that the fate of the Arctic refuge must be debated on its merits, not as part of a sneak attack."

Stevens argued that Congress in 1980 agreed to allow ANWR's oil to be developed at some future date as part an a compromise he supported that expanded the federal refuge to 19 million acres.

It was a commitment, he maintains, that has not been met.

Those who advocate drilling contend the oil — an estimated 1 million barrels a day during peak production — is needed for national security to reduce the country's dependence on imports. Drilling opponents say ANWR's oil would do little to curtail imports.

Steven's proposal would have required the Interior Department to issue its first oil leases in the 1.5-million-acre coastal plain of the refuge within 22 months and another package of leases in 2010. Oil was not expected to flow before 2015.

Developing the Arctic refuge's oil has been one of Bush's top energy priorities and the administration stepped up lobbying for the ANWR provision this week. Interior Secretary Gale Norton has said repeatedly that the oil can be developed without harming wildlife given environmental safeguards in the bill and use of the most modern drilling techniques.

But drilling opponents argued that ANWR's oil should not be exploited because of the coastal plain's fragile ecosystem and wildlife. While the region looks bleak during its long winters, and oil can be seen seeping from some of its rock formations, the coastal strip also is the calving ground for caribou and home to polar bears, musk oxen, and the annual influx of millions of migratory birds.

"Destroying this wilderness will do very little to reduce energy costs nor does it do very much for oil independence," said Sen. Dianne Feinstein, D-Calif.