WASHINGTON – U.S. lawmakers and regulators heaped the blame Thursday on BP PLC, saying its neglect allowed a key oil pipeline in Alaska to become dangerously corroded, causing a leak and forcing the closure of part of the Prudhoe Bay oil field last month.

The former head of pipeline-corrosion monitoring for BP in Alaska refused to testify under oath about the massive oil spill.

The top U.S. regulator for pipelines said BP was warned about the corrosion, but failed to take steps common in the industry to find and mitigate leaks in the pipelines.

The chairman of the full committee, Rep. Joe Barton, R-Texas, said he questioned whether BP should continue to operate the pipeline.

“BP’s policies are as rusty as its pipelines,” Barton said in his prepared speech.

Another congressman, Rep. Gary Welden, R-Ore., said BP stood for “broken pipeline.”

Richard C. Woollam, who was transferred to BP’s Houston offices in 2005 amid concerns that he intimidated potential whistleblowers, invoked the Fifth Amendment of the Constitution in refusing to answer all questions from a House subcommittee.

Other BP executives apologized and pledged to fix operational lapses on the North Slope that led to the region’s biggest ever oil spill in March and the partial shutdown last month of the country’s largest oil field.

Lawmakers said BP’s mistakes in Alaska – as well as its responsibility for a deadly refinery fire last spring – were particularly unacceptable given the industry’s record profits and the relatively inexpensive measures that might have prevented the oil spill.

With Congress aiming to wrap up its current session by the end of the month, Thursday’s House hearing was not expected to result in any specific legislative action; it did, however, offer lawmakers an opportunity to talk tough to Big Oil at a time of soaring prices and ahead of November elections.

Rep. Diana DeGette, D-Colo., said she was especially disappointed in BP, since it professes in advertising to pride itself on protecting the environment. “I applaud BP for trying to move beyond petroleum, but maybe it should start by sticking to the basics and begin to focus on rudimentary pipe maintenance.”

In March, more than 200,000 gallons of oil leaked from a 34-inch pipeline that crosses the Alaska tundra. Follow-up inspections mandated by federal investigators led to the discovery of another much smaller leak, as well as “significant” corrosion, according to BP, which briefly shut down the entire Prudhoe Bay field on Aug. 6.

“It is critical that no further leaks occur on these lines,” Barton said. But, he added, “I’m even more concerned about BP’s corporate culture.”

Lawmakers repeatedly hammered BP executives about allegations that the company failed to adequately address concerns raised by its own pipeline workers over the past five years, in part because of an atmosphere of fear and intimidation under the supervision of Woollam.

Steve Marshall, the president of BP Exploration Alaska Inc., conceded that Woollam’s “abrasive nature” and “intimidation” may have silenced workers.

Federal regulators expressed dismay about BP’s failure to take steps to fix the pipeline, despite signs it needed maintenance.

“We do not understand why (BP) did not address these problems more aggressively much earlier,” said Thomas J. Barrett, administrator of the Pipeline and Hazardous Materials Safety Administration.

After a leak in March raised a red flag about the soundness of the pipelines, “I was dismayed at the slow rate of progress” by the company and its “failure to take actions necessary to ascertain fully the condition of the pipelines,” Barrett said.

In particular, Barrett said he found it “very puzzling that BP did not choose to run cleaning pigs.” Pigs are mechanical devices that clean and inspect the insides of the pipelines.

BP officials said early tests show that oil-eating bacteria may have contributed to the Alaska pipeline corrosion. Excrement from the bacteria inside the pipes produces an acid that eats through carbon steel.

Marshall acknowledged that the corrosion problem could have been mitigated by more consistent inspection and removal of sludge that builds up on the inner walls of oil pipelines, providing shelter for the bacteria.

“Clearly, in retrospect, pigging would have been a positive step we could have taken,” Marshall said.

Marshall said BP’s spending on major maintenance at Prudhoe Bay would rise to $195 million in 2007, a fourfold increase from 2004; $150 million will go toward replacing 16 miles of corroded oil transit lines.

In 2004, BP hired the Houston-based law firm Vinson & Elkins to conduct an internal investigation of alleged workplace harassment and pipeline-corrosion data falsification. The law firm concluded that some pipeline inspectors experienced “fear of retaliation” for reporting safety concerns and other issues, but said there was no evidence that BP employees or contractors were explicitly told not to raise red flags. Vinson & Elkins also found no proof that pipeline corrosion data was falsified.

Woollam, who has worked for BP for 20 years, agreed to undergo counseling while in Alaska. He is now on paid leave.

In an effort to address criticism that the company for years has willfully ignored employee concerns about pipeline safety and other environmental issues, BP on Tuesday asked a former federal judge to serve as its ombudsman and hear complaints from workers in Alaska and elsewhere about the company’s operations.

BP announced Thursday that the company has hired three outside corrosion experts to independently review the Alaska pipeline problems and to make recommendations for improving BP’s corrosion prevention policies.

Robert A. Malone, the head of BP PLC’s U.S. operations, conceded that the company’s reputation has suffered, but he vowed that Prudhoe Bay would be managed in “a safe, efficient and environmentally sensitive way.”

Until last month’s partial shutdown, Prudhoe Bay had been producing roughly 400,000 barrels per day, or 8 percent of total U.S. output. BP is currently pumping 220,000 barrels a day. Marshall said output could be fully restored as early as the end of October.