Instead, in a blistering order that quoted emails from BP’s own lawyers, Judge Barbier rejected the argument and accused BP of trying to “rewrite” the history of the case.

Last month, a divided three-judge panel of the Court of Appeals rejected BP’s argument as well. Claimants already have to sign a form attesting they were hurt by the spill, Judge Southwick wrote. Although “these requirements are not as protective of BP’s present concerns as might have been achievable,” he wrote, “they are the protections that were accepted by the parties and approved by the District Court.”

BP has appealed that decision to the full Court of Appeals.

Mr. Freeh’s operation has meanwhile grown, with scores of employees now taking over a floor in the office building that also houses the claims center. Members of Mr. Freeh’s team have become more closely involved in the center’s operations, with a senior investigator even considered for the role of the center’s chief executive. (Randall Black, a former chief accounting officer for CitiMortgage, was recently named to the post.)

Close inspections of individual claims have grown widespread, and members of Mr. Freeh’s team have been empowered to take back payments deemed illegitimate. Investigators for the center have interviewed Mississippi restaurant owners about where they buy shrimp and tracked down notaries at their homes to confirm signatures. Multiple audits of the claims process have begun or been completed, two by large private accounting firms; this month, the District Court appointed a separate audit committee to advise the program as well.

BP officials say this scrutiny is long overdue to bring rigor to a process that was poorly managed and ethically suspect. Lawyers along the coast say it is discouraging claims.

“They’ve been very successful in getting people to stop filing,” said Robert Couhig, a New Orleans lawyer. “I think a lot of people now say, ‘I don’t want to be a part of this.' ”

Mr. Feinberg, the original man in charge of paying claims, has been watching all of this with dismay. That the settlement has been bogged down so much by acrimony, he said, “too easily leads to the conclusion that an alternative resolution doesn’t work, and in an oil spill you’re better off with an Exxon-Valdez, decades-of-litigation approach. That’s a real public policy missed opportunity.”