Critics of the BLM's recommendation said they were disappointed at what they considered to be a superficial review of the pipeline's age-related problems.

The existing state lease and federal right-of-way grant are scheduled to expire in 2004. The Bush administration has said it considers speedy renewal of those agreements to be an important part of its national energy strategy.

The agreements are with the six oil companies that own the Trans Alaska Pipeline System (TAPS) and its operator, Alyeska Pipeline Service Co. Major owners are BP Plc (BP.L), ConocoPhillips (COP.N) and Exxon Mobil Corp. (XOM.N). Unocal Corp. , Williams Companies Inc. (WMB.N) and Amerada Hess Corp. (AHC.N) own minor shares.

The pipeline carries about 1 million barrels of oil daily, or nearly a fifth of domestically produced oil. It has already shipped more than 13.5 billion barrels of oil, and the BLM estimates it will transport at least another 8.9 billion barrels, not including any possible production from the Arctic National Wildlife Refuge.

The BLM and Department of Interior must wait at least 30 days after the release of the final environmental impact statement before formally extending the right-of-way grant, said BLM spokesman Rob McWhorter.

The environmental impact review was ordered in 1999 by President Clinton's BLM director, Sylvia Baca. Although the pipeline had been in operation since 1979, Baca believed a full environmental review was justified "because of the great import and significance of TAPS," said Rhea DoBosh, spokeswoman for the Joint Pipeline Office, the consortium of federal and state agencies that regulate pipeline operations.

Continued pipeline operations will have some negative impacts, the study conceded.

There is an ongoing risk of oil spills, the study said, both on land and in Prince William Sound, where oil tankers carry crude from the pipeline's Valdez marine terminal.

"Because of improvements to tankers, shipping safety and spill response capability in Prince William Sound developed after the Exxon Valdez incident," another spill of the same magnitude is "unlikely," the study said.

The Exxon Valdez supertanker spilled 11 million gallons in 1989, spreading oil over 1,200 miles of coastline, closing fisheries and killing thousands of marine mammals and hundreds of thousands of seabirds, according to government estimates. It was the worst tanker spill in U.S. waters and the world's deadliest oil spill to wildlife.

But in the future, the largest "likely spill" in marine waters - predicted to occur three times every 100 years, or once during the 30-year renewal period - is 1,700 barrels, the BLM's environmental impact statement said.

More pipeline operations will mean continued air and water pollution and vegetation disturbances, the study predicted, but those effects will be small.

Failing to renew the pipeline's right-of-way grant would mean dismantling the system and ending North Slope oil shipments, the study said. Alaska's oil-dependent economy would be devastated and would not recover to 2003 levels for all of the following 30 years, and national security would be compromised, it said.

Critics of the study said they wanted lease and right-of-way grant renewals to be contingent on new stipulations, such as establishment of a citizens' oversight panel, upgrades of spill prevention and establishment of an escrow account for land rehabilitation after the end of the pipeline's life.