ASHINGTON, April 18 — Undercutting President Bush's energy policy, the Senate sided with environmentalists today and blocked oil and gas drilling in the Arctic National Wildlife Refuge.

With eight Republicans breaking ranks with the president, the decisive vote probably ended, at least for this year, the longtime dream of many Alaskans and conservatives in Washington that the protected wilderness could be opened for development, an issue that has pitted Democrats and environmentalists against Republicans and petroleum interests for more than a decade.

Coming a month after the Senate rejected a Democratic plan to toughen automotive fuel-efficiency standards, today's vote means that the Senate's final energy measure will include modest tax incentives and conservation provisions but no big change in national energy policy.

The vote came on a procedural motion to end debate on the drilling issue, which was presented as an amendment to the comprehensive energy bill. Under Senate rules, Republicans needed 60 votes to win. But they could not even get a majority, and the motion failed 46 to 54.

In addition to the 8 Republicans, 45 Democrats and Senator James M. Jeffords of Vermont, an independent, voted against ending the debate. Forty-one Republicans and five Democrats voted to bring the wildlife refuge measure to a vote.

Later, with hardly any debate, the Senate voted, 88 to 10, to end oil imports from Iraq until the president certified that resumption would be in the national interest. The measure allowed senators to cast a presumably popular vote and has little practical consequence. Saddam Hussein has stopped oil exports, at least temporarily, to protest United States support of Israel.

The House passed an energy bill last year that would permit drilling in the Alaska wilderness area. But Republican leaders acknowledged that today's vote showed that if the House-Senate conference committee on energy legislation adopted a drilling provision, it would be defeated in the Senate.

"What was proved today is we need more Republicans in the United States Senate," Senator Frank H. Murkowski of Alaska, the measure's chief sponsor, said after the vote.

Mr. Murkowski promised that the issue would not go away. "Sooner or later, this nation is going to open up ANWR," he said.

Mr. Bush made oil and gas exploration in the wildlife refuge the central element of his energy policy in his campaign two years ago and in his proposals as president.

In a statement last month, the White House said the area in Alaska was "by far the largest untapped source of domestic petroleum potential." Oil and gas there, the statement continued, "would equal nearly 40 years of imports from Iraq."

Some experts dispute these figures.

At the White House today, Ari Fleischer, President Bush's spokesman, said: "The Senate today missed an opportunity to lead America to greater energy independence. The president will continue to fight for the tens of thousands of jobs that are created by opening ANWR, as well as, more importantly, for the need for America to be able to achieve more energy independence that would result from opening ANWR."

Democrats and environmentalists were gleeful.

"We've sent this misguided plan to the refinery," said Senator Joseph I. Lieberman of Connecticut, one of the leaders in the fight against the drilling amendment.

William Meadows, president of the Wilderness Society, called it "the conservation vote of the new century," and Mark Van Putten, president of the National Wildlife Federation, said the vote presaged "an energy future based on conservation, efficiency and the development of alternatives to burning fossil fuels."

Before the crucial vote today, the Senate rejected, 64 to 36, a proposal that would have permitted exploration in the wildlife refuge and earmarked a portion of the revenues to pay health and other benefits of retired steelworkers. The proposal was a ploy to get additional senators from steel-producing states to support drilling in Alaska, but it failed to do that and lost the votes of several Republicans opposed to what they saw as a bailout of steel companies.

The Arctic wildlife area was established by President Dwight D. Eisenhower in 1960, the year after Alaska became a state, and was expanded in 1980.

Proponents of development in Alaska have worked for years to open the remote tundra's 1.5-million-acre coastal plain for oil and gas exploration. Government geologists have estimated that 6 billion to 12 billion barrels of oil could probably be produced there, depending on the price. The country uses about 7 billion barrels of oil a year, nearly two-thirds of it imported.

Other parts of the country — including unrestricted areas in Alaska, the Rocky Mountain states and the Gulf of Mexico — may be more promising in terms of the amount of new oil that can be produced at a reasonable price, but the Alaska wildlife refuge has become a political touchstone in the running battle between ideological conservatives and environmentalists.

In 1991, a proposal to allow exploration was killed in a filibuster in the Senate. In 1995, one was included in a big budget bill that was vetoed by President Bill Clinton.

This year, the measure's sponsors argued that the terrorist attacks on Sept. 11, the turmoil in the Middle East and rising gasoline prices underscored why it was so crucial to drill in Alaska and make the country less dependent on imported oil.

In his final speech before the votes today, Mr. Murkowski made those points and added, "A vote for this amendment is a vote for the native people of Alaska."

He said he found it unconscionable that the Senate would deal with an energy bill that had no increase in domestic production. He also attacked "so-called environmentalists" who, he said, were concerned about raising money for their organizations and "not interested in the health of this planet or the people of my state."

Mr. Murkowski, who is running for governor in November, held the Senate floor for hours on Wednesday night, speaking to an almost empty chamber, making the same points and showing the same posters over and over. Presumably, he wanted to stay on television until his constituents, most of them four hours behind Washington, got home from work.

Mr. Murkowski's opponents argued that the situation in the world today was irrelevant to question of drilling in the wildlife refuge, since even if exploration began today, no new oil or gas would be available for many years.

In his final speech today, Mr. Lieberman stuck to the environmental argument. Ninety-five percent of the North Slope of Alaska was already open to drilling, he said, and the protected wildlife refuge was "the heart of a thriving, beautiful ecosystem."

Any drilling there, he said, would "irreversibly damage this national treasure," and, at best, it would allow the proportion of the country's oil that was imported to drop to 60 percent from 62 percent.