A federal judge has approved a $75 million settlement of claims that American Express defrauded its cardholders when converting charges made in foreign currencies.

Judge Cecilia Altonaga granted the approval despite objections from several law firms and a prominent New York law professor, all of whom argued that the deal was unfair and may have been the product of collusion between the company and plaintiffs’ attorneys.

In a 47-page ruling issued Tuesday, the Miami-based judge declared that the settlement is “fundamentally fair, adequate and reasonable.” If the pact is implemented, American Express is expected to pay about $63.5 million to cardholders and up to $11 million in fees and costs to the plaintiffs’ lawyers who negotiated the settlement.

The deal would end at least 10 class action lawsuits American Express was facing over its handling of foreign currency transactions. Some accused the company of failing to disclose clearly the 1% or 2% service fee imposed on charges made in foreign currency. Other suits claimed that American Express always used the worst rate of the day to bill card members, and sometimes boosted its take by arbitrarily changing to rates used by MasterCard and Visa.

The move to settle all the claims before Judge Altonaga drew the ire of attorneys involved in some of the suits. The objecting lawyers said the New York firm that cut the deal with American Express, Garwin, Bronzaft, Gerstein & Fisher, was focused on the 1% to 2% service fee to cardholders – or “members,” as American Express calls them – and knew little about the other allegations. The objectors also charged that when American Express had difficulty settling the case with one set of plaintiffs’ lawyers, it moved on to another, a process that has been criticized in legal circles as a “reverse auction.”

The lawyers attacking the deal, who also have a financial interest in keeping their own cases alive, hired a law professor, Samuel Isaacharoff, to weigh in against the settlement. Mr. Isaacharoff, who recently decamped to New York University from Columbia, called the negotiations that led to the deal “whipsawed.”

“The most striking and disturbing feature of the present proposed settlement is that the release reaches claims that were never pleaded in the underlying action and were negotiated away without any effort to assess their value,” the professor wrote in a declaration filed with the court. He expressed concern that the company might be seeking “to buy peace by cutting a deal with the weakest potential class counsel, there by offering a windfall to lawyers who had no leverage in the case, other than the willingness to settle cheap.”

While Judge Altonaga approved the settlement, she also expressed misgivings about how the deal was reached. She noted with some disdain that lawyers for American Express helped the plaintiffs’ lawyers who settled the case draft an amended complaint that included allegations not previously raised by those lawyers. The judge called that practice a “seeming irregularity” and “less than desirable,” but she concluded that the unusual interaction should not derail the agreement. “The procedural agreement here does not necessarily lead to a conclusion that there was collusion among the parties,” she wrote.

A spokeswoman for American Express, Judy Tenzer, did not respond to specific questions about the litigation. “We’re pleased to have the settlement approved,” she said. Under terms of the agreement, the company did not admit to any wrongdoing.

One of the key plaintiffs’ lawyers who argued on behalf of the deal, Bruce Gerstein, declined an interview request yesterday. Mr. Gerstein is no relation to this reporter.

One provision in the agreement bars the settling lawyers from discussing its terms.

Judge Altonaga, who was appointed to the bench by President Bush in 2003, said one factor in her decision to accept the settlement was that the claims asserted in all the lawsuits were “weak” and that the company’s defenses “present a significant hurdle to any potential recovery.” She noted that while the conversion fee of 1% to 2% was not noted on monthly statements at the time, it was in the small print of cardholder agreements. The judge said she was not convinced the company had a duty to disclose how it picked rates to use to convert charges. “No law or contract has been cited that prohibits the making of profit on the buying or selling of currency,” Judge Altonaga wrote. “Where a claim has little to no merit, there is likely to be little to no recovery.”

The judge said that even if American Express were found liable, there might be no damages awarded because other companies charge currency exchange fees that are similar, if not higher. She also said mandatory arbitration provisions in cardholder agreements could have caused some or all of the lawsuits to be thrown out of court.

More than 800,000 customers and former customers of American Express submitted claim forms by an April deadline.

One of the attorneys who asked Judge Altonaga to reject the deal, David Stellings, said he plans to file an appeal. That is likely to delay any distribution of the settlement fund for a year or more.

Mr. Stellings, a partner in the New York office of Lieff, Cabraser, Heimann & Bernstein, said the key issue was not whether American Express profited, but whether it accurately explained its exchange rates to members. “Yes, everyone can make a profit, but you can’t make a profit doing something after you tell people you’re not doing that,” he said. American Express “was just adding on one percent to every payment in certain countries and at certain times without telling anyone about it, just so Amex would make as much money as Visa and MasterCard,” the lawyer said.

In an interview yesterday, Mr. Isaacharoff said he disagreed with Judge Altonaga’s decision. He said he continues to believe the entire array of foreign-transaction cases against American Express may have been worth a lot more than $75 million, a figure he described as the product of “a gestalt assessment.”

“I think people can’t know because the process of negotiations were, in my view, compromised,” he said.

The suits against American Express were filed after a California judge ruled against Visa and MasterCard in a similar case in 2003. That decision, which is under appeal, could result in refunds of as much as $800 million to cardholders, lawyers said.

The class covered by the settlement includes American Express cardholders who used the card overseas between 1997 and 2004.