The Supreme Court yesterday struck down a federal law that prohibits the mailing of unsolicited advertisements for contraceptives, saying that "the level of discourse reaching a mailbox simply cannot be limited to that which would be suitable for a sandbox."

The quote, in the unanimous opinion written by Justice Thurgood Marshall, referred to the government's argument that the law was necessary in part to protect children from seeing the ads for prophylactics.

Neither that reason nor the need to shield adults from such materials justified banning otherwise legal ads from the mails, the court ruled.

The decision in Bolger vs. Youngs Drug Products Corp. was based on the First Amendment protections that the court has carved out in recent years for "commercial speech," such as advertising. The case stems from a challenge to the law by a company that sells contraceptives.

"We have never held that the government itself can shut off the flow of mailings to protect those recipients who might be potentially offended," the court said.

Those who object to the materials can "avert their eyes" or throw them out, Marshall said. The " 'short though regular journey from the mail box to trash can is an acceptable burden, at least so far as the Constitution is concerned,' " Marshall said, quoting a previous court ruling.

"The justifications offered by the government are insufficient to warrant the sweeping prohibition on the mailing of unsolicited contraceptive advertisements," the court said.

Justice William H. Rehnquist, joined by Justice Sandra Day O'Connor, agreed with the opinion but gave different reasons.