ASHINGTON, June 21 — The Supreme Court on Monday unanimously rejected efforts by states to give patients in managed care a right that Congress has so far declined to provide: the ability to sue managed-care companies for damages for refusing to cover treatment that a doctor has deemed medically necessary.

The court ruled, in an opinion by Justice Clarence Thomas, that the laws of Texas and nine other states are pre-empted by the federal law known as Erisa, which applies to the employment-based health care plans that cover some 140 million people.

The law, the Employee Retirement Income Security Act of 1974, allows patients to sue for reimbursement of denied benefits, but not for damages stemming from the denial. A conventional medical malpractice suit, consequently, is not permitted against a typical health maintenance organization or managed- care company under the federal law.

The question for the Supreme Court was whether that prohibition left any maneuvering room for the states, and the court's answer was no. Any state law that "duplicates, supplements or supplants" the remedy available under the federal law "conflicts with the clear Congressional intent to make the Erisa remedy exclusive," Justice Thomas said.

As Justice Ruth Bader Ginsburg indicated in a concurring opinion, the result returns the issue to Congress. "A regulatory vacuum exists," Justice Ginsburg said in an opinion that was also signed by Justice Stephen G. Breyer.

For years, Congress has wrestled with but failed to pass a national "patients' bill of rights."

The decision came in a pair of closely watched cases from Texas, where a strong patients' rights bill became law in 1997 without the signature of George W. Bush, who was then governor. During his campaign for the presidency four years ago, Governor Bush embraced the state law, citing it as a product of his nonpartisan leadership and as a potential model for the country. Arizona, California, Georgia, Maine, New Jersey, North Carolina, Oklahoma, Washington and West Virginia have adopted similar laws.

Before the Supreme Court, the Bush administration opposed the Texas law, instead joining two managed-care companies, Aetna Health Inc. and Cigna HealthCare of Texas Inc. in their appeal of a federal appeals court's ruling that the Texas Health Care Liability Act and the federal law could coexist.

The United States Court of Appeals for the Fifth Circuit, in New Orleans, held in 2002 that the damage suits brought by two managed-care patients were not the type of lawsuit that Congress had intended to pre-empt. While Erisa would bar a breach of contract suit for a denial of benefits, the appeals court said, Congress had not intended to pre-empt a damage suit based on a "duty of ordinary care" as defined in state law.

One of the plaintiffs, Ruby Calad, had a hysterectomy and other abdominal surgery under her husband's health care plan provided by his employer. The plan, managed by Cigna, provided for a one-day hospital stay for a hysterectomy. Ms. Calad's surgeon recommended a longer stay, but the Cigna discharge nurse refused to authorize it. Ms. Calad developed complications at home and had to return to the emergency room several days later.

The other plaintiff, Juan Davila, was prescribed Vioxx, an expensive anti-inflammatory medication, for arthritis and other medical problems. But his health care plan, managed by Aetna, authorized Vioxx only for patients who had first tried and failed to benefit from two less expensive drugs. One of those drugs, Naprosyn, causes a higher incidence of gastrointestinal bleeding, a complication that brought Mr. Davila within hours of dying. He needed seven units of blood and was in critical care for five days.

In his majority opinion, Justice Thomas offered a spare one-paragraph description of the facts of the two cases, Aetna Health Inc. v. Davila, No. 02-1845, and Cigna HealthCare of Texas Inc. v. Calad, No. 03-83. He said that in any event the plaintiffs' injuries could not fairly be attributed to their managed-care companies if those companies "correctly concluded that, under the terms of the relevant plan, a particular treatment was not covered."

The cause of the injuries was "the failure of the plan itself to cover the requested treatment," Justice Thomas said, reflecting the managed-care industry's argument that it should not be blamed when an employer has, for economic reasons, declined to buy a certain level of coverage.

The court's unanimity was not reflected in responses to the decision. The American Medical Association, whose members often find themselves in conflict with managed-care companies, said that it was "extremely disappointed" by the decision. "Managed-care plans can now practice medicine without a license, and without the same accountability that physicians face every day," the association's statement said.

But a trade organization for managed-care companies called America's Health Insurance Plans called the decision "a victory for consumers and employers" that "puts the brakes on efforts by trial lawyers to turn every question about the scope of an individual's coverage into a costly lawsuit." The American Benefits Council, representing employers, likewise said the decision would protect the ability to offer cost-effective health care coverage.

Democratic members of Congress were quick to react and to criticize the Bush administration. Representative John D. Dingell of Michigan, the ranking Democrat on the House Energy and Commerce Committee, said he would reintroduce the "patients' bill of rights" measure that was passed by the Senate in 2001. The House version of the bill had more limits on patients' lawsuits, among other differences with the Senate version, and the two were never reconciled.

Senator John Kerry of Massachusetts, the presumptive Democratic presidential nominee, has said that as president he would support "a real patients' bill of rights."

Miguel A. Estrada, the lawyer who argued in the Supreme Court for Aetna and Cigna, said in an interview that patients like Ms. Calad and Mr. Davila could try a range of administrative remedies under regulations issued by the Department of Labor that require a prompt response if the physician complains about the denial of necessary treatment.