WASHINGTON – President Bush’s goal of opening the national wildlife refuge on Alaska’s northern coast to oil drilling now has its best chance yet of success in Congress, thanks to the election of four additional supporters in the Senate whose votes could reverse a razor-thin margin that defeated a drilling measure last year.

The proposal to open 2,000 acres of the Arctic National Wildlife Refuge is part of a broader energy policy advocated by the White House that is aimed in part at reducing American dependence on foreign oil. Both the environmental impact of the policy and the amount of oil it would produce are disputed by both sides in the ongoing debate.

Supporters say it would produce enough domestic oil to replace imports from Saudi Arabia for 25 years. Environmentalists, however, say the plan will produce a modest amount of oil while interfering with the nesting of birds and the calving of caribou. Senate opponents blocked the measure on a 48-52 vote last year, but supporters believe the balance has now reversed in favor of the proposal. They say the coming year is the best chance yet for getting approval for drilling, with a 55-44-1 GOP majority in the Senate.

“We are much more optimistic given the changes in the makeup in the Senate,” a spokesman for the House Committee on Resources, Brian Kennedy, said. “We expect something to come up early in the congressional session. With a few new votes in the Senate, support in the House, and a president who would sign it, we’d like to take advantage of the opportunity.”

The chairman of the committee, Rep. Richard Pombo, predicted last week that Congress will pass an energy plan that includes drilling at the refuge.

The other option – including the measure in budget legislation – would require only 51 votes to pass, and it would be immune from filibusters, which require 60 votes to overcome.

Senator Domenici, a Republican of New Mexico and chairman of the Senate Energy and Natural Resources Committee, has said he will press for the measure in budget deliberations.

“With oil trading at nearly $50 a barrel, the case for ANWR is more compelling than ever,” Mr. Domenici told the Associated Press. “We have the technology to develop oil without harming the environment and wildlife.”

That optimism was echoed by Kevin Hand, the executive director of Arctic Power, a nonpartisan group that lobbies in favor of developing the land. “We believe this can be the year – and that it will be the year – that we get ANWR through Congress,” he said.

Last month’s election brought four new supporters of the proposal to the Senate, including three Republicans who had voted for the measure while they were in the House of Representatives: Rep. John Thune of South Dakota, Rep. Jim DeMint of South Carolina, and Rep. Richard Burr of North Carolina. Another Republican, Mel Martinez of Florida, expressed support for the measure during his campaign. The outgoing secretary of Energy, Spencer Abraham, has said that “the votes are there” and that he expects the measure to be passed in the next Congress.

Mr. Kennedy predicted that the measure would likely follow both legislative tracks – as part of the comprehensive energy package that has been passed numerous times in the House only to fail in the Senate, and also as part of a budget reconciliation bill. In the latter case, the House Committee on Resources could include in its expected revenues the royalties and “bonus bids” for land leases in ANWR, thereby making them a part of the budget, Mr. Kennedy said.

However, with the Senate so closely divided, he and other supporters of the bill temper their excitement with cautions that the fate of the measure could still be tripped up in various congressional procedures.

A foremost advocate of the proposal in the Senate, Senator Stevens of Alaska, is “hopeful” but cautious about its prospects, according to his press secretary, Courtney Schikora. “Clearly ANWR is a priority for the Alaska congressional delegation and we are happy the Senate is comprised of 55 Republicans. However, we have not elaborated on when and whether ANWR will come to a vote in the 109th congress,” she said.

One concern is that if supporters at tempt to include ANWR in the 2006 federal budget, opponents may try to invoke the so-called Byrd rule, named after Senator Byrd, a Democrat of West Virginia. The rule allows an opponent to challenge the inclusion of policy legislation in a budget bill, and it requires 60 votes to overcome the challenge, which would render the measure “much more difficult to pass,” Mr. Hand said.

Critics of Alaskan drilling are preparing to rally opposition to the inclusion of ANWR in the budget bill, even from those who are supporting the measure.

“Proponents of oil drilling have indicated they may attempt a backdoor scheme in the budget. It’s important that members of Congress are reminded that this is not a budgetary issue and that the budget should not be used for controversial issues,” said a spokeswoman for the Sierra Club of Alaska, Betsy Goll.

The Sierra Club expects some lawmakers who are otherwise in favor of the drilling to vote against putting the measure in the budget. “We’ll have their support against that, because it doesn’t belong there,” Ms. Goll said.

Not everyone agrees. Mr. Kennedy said Senate precedent favors the inclusion of the measure in the budget after the Senate parliamentarian ruled in favor of it in 1995. That year both the House and Senate passed the measure before it was vetoed by President Clinton.

While critics of ANWR legislation say it would produce little energy at great ecological cost – only six months’ supply of oil, by some accounts – advocates counter that the six-month figure underestimates the supply and assumes that the ANWR oil would replace all other oil supplies, rather than imports from one source, such as Saudi Arabia.

Supporters add that those studies estimated that 6 billion to 16 billion barrels would be extractable from the land and assumed a crude oil price of $25 per barrel.

At higher prices, even larger quantities would become economical to extract, they said.

Crude oil closed at $41.82 a barrel on the New York Mercantile Exchange yesterday.