It is not necessarily unlawful for an employer to adopt policies that put older workers at a disadvantage. Such policies pass muster under the Age Discrimination in Employment Act as long as they are based on “reasonable factors other than age.”

The question in a Supreme Court argument on Wednesday was whether the employer has to prove that such “reasonable factors” exist, or whether it is up to the employee who has brought a lawsuit to show that they do not.

The burden of proof makes a substantial difference in any lawsuit, although statutes rarely specify which side bears it. For federal laws against race and sex discrimination in the workplace, the Supreme Court has filled the gap by developing fairly elaborate procedures that plaintiffs and defendants must follow. But for age discrimination, the rules have remained murky, leaving the lower courts in confusion over how to handle this rapidly growing category of workplace discrimination claims.

The argument the justices heard on Wednesday was in a case brought by two dozen workers at a federal research laboratory in upstate New York. Carrying out a reduction in force, the employer, Knolls Atomic Power Laboratory, which is owned by the Lockheed Martin Corporation, terminated 31 employees after using a set of guidelines to evaluate workers’ skills and amenability to retraining. All but one dismissed employee was over 40, the age at which the protections of the federal age discrimination law begin to apply.

Most of the affected employees joined a lawsuit arguing that there was no justification for using an evaluation system that had such a starkly disparate impact on older workers, and that the procedure consequently violated the federal law. The plaintiffs won in a jury trial. But the judgment was overturned by the United States Court of Appeals for the Second Circuit, in Manhattan, which held that plaintiffs in such a case had the burden of showing that the policy they were challenging was unreasonable.

The unanimous decision comes in a case from Portsmouth, Va., where city detectives seized crack cocaine from a motorist after arresting him for a traffic ticket offense.

David Lee Moore was pulled over for driving on a suspended license. The violation is a minor crime in Virginia and calls for police to issue a court summons and let the driver go.

Instead, city detectives arrested Moore and prosecutors say that drugs taken from him in a subsequent search can be used against him as evidence.

"We reaffirm against a novel challenge what we have signaled for half a century," Justice Antonin Scalia wrote.

Scalia said that when officers have probable cause to believe a person has committed a crime in their presence, the Fourth Amendment permits them to make an arrest and to search the suspect in order to safeguard evidence and ensure their own safety.

Moore was convicted on a drug charge and sentenced to 3 1/2 years in prison.

The Virginia Supreme Court ruled that police should have released Moore and could not lawfully conduct a search.

State law, said the Virginia Supreme Court, restricted officers to issuing a ticket in exchange for a promise to appear later in court. Virginia courts dismissed the indictment against Moore.

Moore argued that the Fourth Amendment permits a search only following a lawful state arrest.

In a concurring opinion, Justice Ruth Bader Ginsburg said she finds more support for Moore's position in previous court cases than the rest of the court does. But she said she agrees that the arrest and search of Moore was constitutional, even though it violated Virginia law.

The Bush administration and attorneys general from 18 states lined up in support of Virginia prosecutors.

The federal government said Moore's case had the potential to greatly increase the class of unconstitutional arrests, resulting in evidence seized during searches being excluded with increasing frequency.

Looking to state laws to provide the basis for searches would introduce uncertainty into the legal system, the 18 states said in court papers.

New Jersey's Supreme Court found that the state's constitution gives greater protection against unreasonable searches and seizures than the U.S. Constitution.

The court ruled that Internet providers should not disclose private information to anyone without a subpoena.

A Washington lawyer who handles Internet litigation, Megan E. Gray, said the ruling "seems to be consistent with a trend nationwide, but not a strong trend."

"It's contrary to what is happening with rights of privacy at the federal level," Gray said. "But it's all over the board for the states, with a mild trend toward protecting this information."

Grayson Barber, a lawyer representing the American Civil Liberties Union, Electronic Frontier Foundation and the Electronic Privacy Information Center, among other groups that filed friend-of-the-court briefs in the case, said it was the first ruling in the nation to recognize a reasonable expectation of privacy for Internet users.

On Thursday, attorneys for Lisa Miller-Jenkins asked the court to revisit the issue, which was decided in favor of Janet Miller-Jenkins in 2006.

The two Virginia residents were joined in a Vermont civil union in 2000, but later split up. Lisa had a child in 2002 and a Vermont family court awarded Janet visitation rights.

Lisa argues that since Virginia law doesn’t recognize civil unions her former partner shouldn’t have parental rights.

Janet says the case has already been decided in her favor by a family court.