he Supreme Court yesterday struck down a California law designed to help Holocaust survivors receive payment on insurance policies that European companies have long denied, saying that the law improperly interfered with United States foreign policy.

But California officials, several members of Congress and private lawyers said they would increase their efforts to force the companies to publish lists of their Holocaust-era policyholders and to make good on what some Holocaust and insurance experts estimate could be several billion dollars worth of unpaid life insurance policies.

"These companies must still deal with California," said John Garamendi, the California insurance commissioner, who has broad authority to regulate insurers. "I am sure that companies that operate now and wish to continue operating in the fifth-largest economy in the world will do everything they can to address this issue."

The American Insurance Association, which took the case to the Supreme Court on behalf of member companies that are subsidiaries of European insurers, said it was gratified by the decision. But in response to Mr. Garamendi's remark, a spokeswoman, Nicole Mahrt, would only say, "We'll have to review any decisions or actions he takes."

The California governor, Gray Davis, said in a statement that he would do "everything in my power to bring some measure of peace to survivors and victims' families."

Writing for the majority in the 5-to-4 decision, Justice David Souter said letting the California law stand would "hamstring the President's settling international controversies."

The California law, adopted in 1999, required the subsidiaries of European companies to produce the names of millions of policyholders who bought coverage from their parent companies in Germany, Italy and elsewhere in Europe between 1920 and 1945. Failure to comply could have cost the companies their licenses to do business in the state.

California officials and historians have contended that because documents were lost in the Holocaust and many with knowledge of the insurance died in concentration camps, the only way survivors can know if they are owed money is if the names of policyholders are published.

But the insurers have persistently refused to produce full lists of policyholders. They say European privacy laws bar publication of names, that producing such lists would be costly and that in any case many records have been destroyed — a point disputed by some Holocaust experts.

In both the majority opinion and a dissent written by Justice Ruth Bader Ginsburg, the court noted that during the Holocaust, the German authorities confiscated many life insurance policies and that insurers simply refused to pay claims on many others, sometimes insisting that claimants meet the impossible demand of presenting copies of policies and death certificates. As a result, the court said, the rightful beneficiaries were never paid.

In 1998, facing more than a dozen lawsuits and under the threat from regulators of having their licenses to do business revoked, a half-dozen European insurers agreed to join in the founding of the International Commission on Holocaust-Era Insurance Claims. One goal of the commission, which included regulators and Jewish groups, is the publication of the names of policyholders.

It has so far published on the Internet about 422,000 names, most obtained through a settlement between the United States and Germany over several Holocaust issues. But Holocaust experts say millions of policies remain unaccounted for.

In the settlement with Germany, the United States also agreed to discourage lawsuits or regulatory action against German companies, and it filed a brief in the California case.

For several years, Justice Souter noted, the United States policy has been to try to resolve Holocaust insurance issues through negotiations, rather than litigation or unilateral lawmaking. Washington has regarded the international commission as the proper forum for resolving the insurance disputes. But the commission has been criticized by many people as being ineffectual.

In the decision yesterday, Justice Souter wrote that by trying to force action by the insurance companies, "California seeks to use an iron fist, where the president has consistently chosen kid gloves."

"We have heard powerful arguments that the iron fist would work better," he continued, adding that it was not for the court to decide between the two. Rather, he said, it was the court's task to deal with the conflict over foreign policy.

"The evidence," he concluded, quoting an earlier decision, "is more than sufficient to demonstrate that the state act stands in the way of diplomatic objectives" of the president.

Two lawyers pursuing lawsuits over Holocaust-era insurance policies against Assicurazioni Generali, an Italian company — Linda Gerstel in New York and Bill Shernoff in California — said the decision would not derail their cases. Both have said they hope to obtain full policyholder lists in their litigation.

Earlier this year, four congressmen introduced legislation requiring — or permitting states to require — publication of the lists. One of them, Representative Henry A. Waxman, Democrat of California, said in a statement that he had signed up 50 co-sponsors and that he believed the court's decision "would spur momentum to get more sponsors and move this legislation forward."