Washington ? The Senate narrowly rejected oil drilling in an Alaska wildlife refuge Wednesday as eight Republicans defied party leaders and the White House on an issue at the core of President Bush’s energy agenda.

Drilling advocates said the plan was probably dead for this Congress.

Despite intense lobbying by pro-drilling senators and the Bush administration, Democrats mustered the support needed to strip an oil drilling provision from a budget resolution expected to be approved later this week.

An amendment offered by Sen. Barbara Boxer, D-Calif., to scrap the provision passed 52-48.

Development of the millions of barrels of oil beneath the 100-mile coastal plain of the Arctic National Wildlife Refuge in northeastern Alaska has been at the heart of Bush’s energy plans. Environmentalists contend drilling there would jeopardize a pristine area valued for its wildlife, while the administration views the oil as key to curtailing America’s dependence on imports.

All but five Democrats voted against refuge drilling, but eight Republicans bucked their party. Congress set aside the refuge in 1960 and declared the oil off-limits unless a measure specifically lifted the ban.

How much oil is beneath the refuge’s coastal plain is uncertain because only one exploratory well has been drilled, and its results have not been made public. The Interior Department estimates that the plain could have anywhere from 5.7 billion barrels to 16 billion barrels.

Environmentalists argue that no more than about 3.2 billion barrels is likely to be economical for oil companies to pursue and that some major oil companies have begun to lose interest in the refuge.

The United States uses about 20 million barrels of oil a day.