WASHINGTON – A closely divided Senate voted yesterday to approve oil drilling in an Alaska wildlife refuge, a major victory for President Bush and a stinging defeat for environmentalists who have fought the idea for decades.

By a 51-49 vote, the Senate put a refuge drilling provision in next year’s budget, depriving opponents of the chance to use a filibuster to try to block it. Filibusters, which require 60 votes to overcome, have been used to defeat drilling proposals in the past.

Senator Stevens, an Alaska Republican who has fought for 24 years to open the Arctic National Wildlife Refuge to oil companies, acknowledged it still could be “a long process”before a final drilling measure clears Congress. Lawmakers must agree on the final budget, something they failed to do last year, or yesterday’s vote would have been for naught.

Also, the House did not include an Arctic refuge measure in its budget, a difference that will have to be worked out in future negotiations.

The Senate made clear by yesterday’s vote that a majority now supports tapping what is believed to be 10.4 billions or more barrels of oil within the refuge’s 1.5 million-acre coastal plain, said Senator Murkowski, a Republican of Alaska. Two years ago, a similar attempt to use the budget process to open the refuge failed by three votes.

But that was before Republicans last November expanded their majority, adding a number of GOP senators who favor drilling. Only seven Republicans, all moderates, bucked their party yesterday and voted with most Democrats against opening the refuge.

The oil industry has sought for more than two decades to get access to the oil. In 1980, Congress said the oil could be developed, but only if lawmakers specifically authorized the Interior Department to sell oil leases. Repeatedly Congress has failed to do so.

Environmentalists for years have fought such development, contending it would lead to a spider web of drilling platforms, pipelines, and roads that would adversely impact the calving grounds of caribou, polar bears, and millions of migratory birds that use the refuge’s coastal plain.

“The fact is it’s going to be destructive,” Senator Kerry, a Democrat of Massachusetts, said during debate on an amendment that would have stripped the drilling language from the budget measure. Democrats fell two votes short of the 51 needed.

Mr. Kerry and other drilling opponents argued that more oil would be saved than ANWR could produce if Congress enacted an energy policy focusing on conservation, more efficient cars and trucks, and increased reliance on renewable fuels.

Drilling supporters countered that oil can be pumped while still protecting the environment and wildlife.

Modern technology, drilling techniques, and environmental restrictions would dramatically limit the industrial footprint that would be left on the tundra and protect wildlife, said Ms. Murkowski. “We know we’ve got to do it right. … It’s a fragile environment.”

One GOP senator after another argued that with foreign imports accounting for more than half of the oil the country uses, every available barrel should be pursued. The Alaska refuge represents the largest potential onshore oil find in the country, they said.

“Some people say we ought to conserve more. They say we ought to conserve instead of producing this oil. But we need to do everything. We have to conserve and produce where we can,” said Senator Domenici, a Republican of New Mexico who chairs the Energy and Natural Resources Committee.

But drilling opponents rejected the suggestion that ANWR’s oil would have much impact on global markets, today’s high oil and gasoline prices, or the continued reliance on foreign producers.

“We won’t see this oil for 10 years. It will have minimal impact,” argued Senator Cantwell, a Democrat of Washington. It is “foolish to say oil development and a wildlife refuge can coexist.”

Ms. Cantwell and other Democrats accused Republicans of trying “an end run” by attaching the refuge provisions to the budget, saying the question of drilling in an ecologically pristine refuge – a “special place” as many environmentalists called it – should be debated as separate legislation or as part of a broad energy bill.

“It’s the only way around the filibuster,” Mr. Stevens said, defending the use of the budget process. He said that approach is justified for issues that have special importance such as getting at ANWR’s oil, something he characterized as a matter of “national security.”

While Democrats led the opposition to drilling, three Democratic senators voted with the GOP majority: Senators Akaka and Inouye of Hawaii and Senator Landrieu of Louisiana.

The seven Republicans who voted against drilling were Senators Chafee of Rhode Island; Susan Collins and Olympia Snowe of Maine; Mike DeWine of Ohio, John McCain of Arizona, Gordon Smith of Oregon, and Norm Coleman of Minnesota.