Washington ? The Supreme Court put public high school students on notice Thursday: Drug tests may be required for playing chess or joining the cheerleader squad.

Justices ruled 5-4 that schools’ interest in ridding their campuses of drugs outweighed students’ right to privacy, allowing the broadest drug testing yet of young people whom authorities have no particular reason to suspect of wrongdoing.

The decision gives school leaders a free hand to test students who participate in competitive after-school activities or teams more than half the estimated 14 million American high school students.

Drug tests had been allowed previously just for student athletes.

“We find that testing students who participate in extracurricular activities is a reasonably effective means of addressing the school district’s legitimate concerns in preventing, deterring and detecting drug use,” Justice Clarence Thomas wrote for himself, Chief Justice William H. Rehnquist and Justices Antonin Scalia, Anthony M. Kennedy and Stephen Breyer.

The court stopped short of allowing random tests for any student, but several justices indicated they were interested in answering that question at some point.

Justice Ruth Bader Ginsburg, in a dissent, said the “program upheld today is not reasonable, it is capricious, even perverse.”

The court ruled against a former Oklahoma high school honor student who competed on an academic quiz team and sang in the choir. Lindsay Earls, a self-described “goody two-shoes,” tested negative but sued over what she called a humiliating and accusatory policy. She said Thursday was “a sad day for students in America.”

“I find it very disappointing that the court would find it reasonable to drug-test students when all the experts, from pediatricians to teachers, say that drug testing is counterproductive,” said Graham Boyd, director of drug policy litigation at the American Civil Liberties Union and Earls’ lawyer.

“The best way to prevent drug use is to involve them in extracurricular activities,” Boyd said.

Justice Stephen Breyer, who provided the crucial fifth vote, wrote separately to say he hopes the testing reduces peer pressure and “addresses a serious national problem.”

Ginsburg, joined by Justices John Paul Stevens, Sandra Day O’Connor and David Souter, said extracurricular activities should not be discouraged.

The Bush administration backed the school system in rural Tecumseh, Okla., which had considered testing all students, then settled on testing only those involved in competitive extracurricular activities on the theory that by voluntarily representing the school, those students had a lower expectation of privacy.

The case is Board of Education of Independent School District No. 92 of Pottawatomie County v. Earls, 01-332.