WASHINGTON - Several Supreme Court justices seemed taken aback yesterday at the idea that insurance companies might be required to notify tens of millions of customers that they aren't getting the best rates because of their credit reports.

In making the argument for notification, lawyers for consumers said two insurance companies, Geico and Safeco Corp., had violated the Fair Credit Reporting Act by failing to send customers notices of adverse decisions made because of their credit reports.

Congress passed the credit reporting act in 1970 to protect consumers from flaws in the system and improve the reliability of reports.

At issue is a decision a year ago by the U.S. Circuit Court of Appeals for the Ninth Circuit in San Francisco that would make it easier for consumers to prevail when they sue corporations for failing to notify them that their credit histories may prevent them from getting the lowest insurance premiums.

The appeals court and attorneys for the consumers say the standard for proving violation of the law is reckless disregard of it. The companies say the standard for showing violation is higher: proving that the companies knowingly broke the law.

If the court adopts the consumers' argument, tens of millions of notices will be sent out, Justice Stephen Breyer said.

Regarding the expansive notification views, "I don't understand where that comes from," Justice Samuel Alito said.

That is what the law requires, came the response from Scott Shorr, an attorney for some consumers suing the companies.

The system's cornerstone is consumers' monitoring their credit reports for accuracy. Consumer groups say the insurance companies are weakening the system by looking for ways to avoid notifying customers when their credit reports are used in making a decision.

"Consumers who do not receive an adverse-action notice . . . do not learn of their right to a free credit report to check its accuracy," a half-dozen advocacy groups said in court papers.

One consumer represented in the case, Ajene Edo of Portland, Ore., applied for auto insurance. Geico concluded that Edo did not qualify for its coverage for low-risk customers. Instead, it offered to insure him, but as a moderate-risk customer.