The Supreme Court ruled unanimously yesterday that states can be barred from disclosing the personal information drivers provide to obtain a license, in a surprising decision immediately extolled by privacy activists and civil libertarians.

Deciding a closely watched dispute that particularly evoked privacy fears in today's world of instant electronic data, the justices upheld a federal law that forbids states from selling addresses, telephone numbers and other information that drivers put on license applications.

The ruling was an unexpected departure from the court's recent string of rejections of federal laws that touch on state activities. But Chief Justice William H. Rehnquist emphasized how this law was different and encroached far less on state authority.

Women's groups and civil libertarians praised the decision for preserving a 1994 law that they say keeps intimate information from stalkers and harassers. Privacy advocates and members of the direct-marketing industry agreed the ruling opens the way for Congress to pass similar laws restricting the interstate sale of records on land ownership, housing sales, occupational and recreational licenses and an array of other information.

That could mean that even as the details of people's lives become more avidly collected by marketers and more readily available through the Internet, widespread access will not go unchecked. "It's clearly a message to the states they're going to have to be much more careful," said Marc Rotenberg, director of the Electronic Privacy Information Center.

Yesterday was a full and dramatic day at the nation's highest court, as the justices ruled in four other cases--from criminal law to environmental protections--and heard arguments on grandparents' visitation rights.

Congress passed the Driver's Privacy Protection Act (DPPA) six years ago, motivated in part by the death of actress Rebecca Schaeffer, who was killed at her California home by a stalker who had traced her address through the motor vehicles division.

More broadly, lawmakers were addressing public concerns about telemarketers, the media and others with access to the vast array of personal information in the records of state motor vehicle departments. Congress found that many states were making millions of dollars a year selling the information, which can include Social Security numbers, medical information and photographs.

The DPPA bars states from disclosing such personal information without drivers' consent. There are exceptions in the law for matters of motor vehicle and driver safety, theft, and manufacturers' product recalls--and one of the states' complaints was that the statute was difficult to administer.

In yesterday's case, South Carolina, backed by a dozen other states, challenged the law as an unconstitutional encroachment on its business; the state had a policy making DMV records available to anyone who filled out a form and paid the requisite fees. The U.S. Court of Appeals for the 4th Circuit agreed, saying the law wrongly forced states to administer a federal regulation and violated federalism principles.

But in reversing the Richmond-based 4th Circuit yesterday, the high court emphasized that, unlike past laws ruled unconstitutional, the privacy statute wasn't telling states to pass specific legislation or to regulate their citizens in particular ways.

In a relatively brief 10-page opinion in Reno v. Condon that drew no dissent or concurring statements, Rehnquist wrote that the law flowed from Congress's authority to regulate interstate commerce.

Addressing the larger question about the federal-state boundary, Rehnquist explained how the act differs from two statutes--concerning handgun purchase waiting periods and environmental rules--struck down in the 1990s. "The DPPA regulates the states as owners of databases. It does not require the South Carolina legislature to enact any laws or regulations, and it does not require state officials to assist in the enforcement of federal statutes regulating private individuals."

The court's ruling turned on an analysis of Congress's interstate commerce powers, but most of the reaction yesterday addressed larger privacy questions. Sen. Barbara Boxer (D-Calif.), a sponsor of the law, said the decision permits Congress to protect "information that could be used to harm our citizens."

Eleanor Smeal, president of the Feminist Majority Foundation, noted that some antiabortion protesters have tracked physicians and their patients through motor vehicle information. "This Supreme Court decision will save the lives of both abortion providers and women targeted by stalkers," she said.

But South Carolina Attorney General Charles Condon declared, "A one-size-fits-none attempt by the federal government to protect privacy will not work."

And H. Robert Wientzen, president of the Direct Marketing Association, expressed concerns that important business information on which his group's members rely will dry up. He said the association will ask Congress to hold hearings on the matter.

In a separate ruling yesterday, the court, voting 7 to 2, upheld citizen groups' right to sue alleged polluters under the Clean Water Act even though any financial damages awarded would be paid to the federal government.

"This is a rare victory for the environment from the Supreme Court and a dramatic reversal of the trend of Supreme Court decisions on citizens' rights to sue under environmental laws," John Echeverria, director of the Environmental Policy Project at Georgetown Law Center, said of the ruling in Friends of the Earth vs. Laidlaw Environmental Services.

Staff writer Robert O'Harrow contributed to this report.