Congress had its eye on voters more than the Constitution when it banned the $2 billion "dial-a-porn" business last election year, an attorney for one of the larger telephone message services told the Supreme Court.

But a Justice Department lawyer arguing in favor of banning all dial-up services offering sexually explicit telephone messages says the law is needed to "protect children from hearing patently offensive speech."The court, which heard arguments Wednesday in a California case, must determine whether the lawmakers can issue an outright ban that fails to distinguish between indecent and obscene material.

The justices will also be looking at whether technological safeguards exist to prevent children from dialing the service's 976 numbers. The 976 exchanges also are used for other, non-controversial types of messages such as sport scores, time checks and weather reports.

Born in 1983, the dial-a-porn industry matured quickly. In 1984, Justice Department Richard Taranto said, 180 million such calls were placed by customers in New York alone. The industry's income last year topped $2 billion, he said.

Harvard law professor Laurence Tribe, representing a dial-a-porn service known as Sable Communications, said the availability of technical safeguards "makes this flat ban illegitimate."

When Justice Byron R. White asked Tribe why Congress passed the total ban, Tribe responded, "That's not a hard question, it was an election year."

"I didn't say it was hard," White said as laughter filled the courtroom.

The total ban on dial-a-porn never was imposed because a federal judge in California ruled that the 1988 law could be applied only to obscene, not merely indecent, phone messages.

U.S. District Judge Wallace Tashima in Los Angeles said outlawing non-obscene messages, even though they may be inappropriate for minors, violates the free-speech protections of the Constitution's First Amendment. The government appealed the ruling to the Supreme Court.

Justice Sandra Day O'Connor said Wednesday she doubted whether the proposed ban meets the "least restrictive means" test the court has used when scrutinizing governmental interference based on speech content.