federal judge yesterday dismissed several charges against the nation's largest health insurance companies, but he said plaintiffs could proceed with accusations that the insurers had violated federal fraud and pension laws.

Judge Federico Moreno of the United States District Court in Miami ruled that plaintiffs representing many health plan subscribers could proceed with claims of fraud under RICO, the Racketeer Influenced and Corrupt Organizations Act, against Aetna (news/quote), Cigna (news/quote) and United Healthcare. Humana (news/quote) is also a RICO defendant under a ruling by Judge Moreno last year.

Fraud claims were dropped against two other companies, the Prudential units of Aetna in California and Virginia, and Health Net (news/quote), formerly Foundation Health Systems, in Florida. Aetna remains a defendant in other states, and both Aetna's Prudential units and Health Net remain defendants in fraud suits filed by doctors and medical societies.

Judge Moreno is weighing the issues raised in consolidated lawsuits that accuse the companies of conspiring to deny care and of withholding information about the business reasons for medical decisions. Roughly 50 lawsuits across the country have been filed against the managed care companies.

Judge Moreno said plaintiffs in California, Florida, Virginia and New Jersey were barred from making RICO claims against health insurers because of the structure of insurance fraud laws in those states. He did not specify the states in which RICO claims could now proceed, but defense lawyers suggested that plaintiffs in Texas and Mississippi, and possibly many other states, could still pursue such cases.

Judge Moreno also said the plaintiffs could proceed with claims that the health insurers violated the pension law that governs them, the Employee Retirement Income Security Act, or Erisa. The plaintiffs said the insurers had done so by interfering with physician-patient relationships.

But the judge dismissed claims that the insurers had violated pension laws by misrepresenting the "medical necessity" for actions that the plaintiffs argued were taken for nonmedical financial reasons. While former members of health plans could still claim violations of pension laws on these grounds, Judge Moreno said current health plan members could use administrative channels to appeal decisions on the medical necessity of different treatments.

Spokesmen for both sides said that they were pleased by yesterday's ruling. "We can now move forward with the core claims," said Stephen Neuwirth, a plaintiffs' lawyer with the law firm of Boies, Schiller & Flexner.

David Carter, a spokesman for Aetna, said the company regarded the ruling as "a significant narrowing of the plaintiffs' claims."

Stephanie Kanwitt, an executive vice president of the Association of American Health Plans, an insurers' trade group, said the ruling had reduced the plaintiffs' cases to "a shadow of their former self."

Lawyers on both sides said the next important step would be a decision on whether the lawsuits would be accorded class-action status.

In a ruling on Feb. 13 that lawyers for the defendants said was an important precedent, the United States Court of Appeals for the 11th Circuit in Atlanta, which hears appeals in federal cases from Florida, said that plaintiffs in a case involving fraudulent telephone calls "bear the burden" of proving that each person was damaged. Insurance company lawyers said in a legal brief filed this week that the ruling in that case, Sikes v. Teleline Inc., showed that the plaintiffs in the health insurance cases could not establish a class.

But Mr. Neuwirth said the plaintiffs believed that the Sikes ruling did not change "existing law that we were relying on" in seeking court approval for a class action.