WASHINGTON – The Supreme Court tightened limits on student speech Monday, ruling against a high school student and his 14-foot-long “Bong Hits 4 Jesus” banner.

Schools may prohibit student expression that can be interpreted as advocating drug use, Chief Justice John Roberts wrote for the court in a 5-4 ruling.

Joseph Frederick unfurled his homemade sign on a winter morning in 2002, as the Olympic torch made its way through Juneau, Alaska, en route to the Winter Olympics in Salt Lake City.

Frederick said the banner was a nonsensical message that he first saw on a snowboard. He intended the banner to proclaim his right to say anything at all.

His principal, Deborah Morse, said the phrase was a pro-drug message that had no place at a school-sanctioned event. Frederick denied that he was advocating for drug use.

“The message on Frederick’s banner is cryptic,” Roberts said. “But Principal Morse thought the banner would be interpreted by those viewing it as promoting illegal drug use, and that interpretation is plainly a reasonable one.”

Morse suspended the student, prompting a federal civil rights lawsuit.

Students in public schools don’t have the same rights as adults, but neither do they leave their constitutional protections at the schoolhouse gate, as the court said in a landmark speech-rights ruling from Vietnam era.

The court has limited what students can do in subsequent cases, saying they may not be disruptive or lewd or interfere with a school’s basic educational mission.

Frederick, now 23, said he later had to drop out of college after his father lost his job. The elder Frederick, who worked for the company that insures the Juneau schools, was fired in connection with his son’s legal fight, the son said. A jury recently awarded Frank Frederick $200,000 in a lawsuit he filed over his firing.

Joseph Frederick, who has been teaching and studying in China, pleaded guilty in 2004 to a misdemeanor charge of selling marijuana at Stephen F. Austin State University in Nacogdoches, Texas, according to court records.

Conservative groups that often are allied with the administration are backing Frederick out of concern that a ruling for Morse would let schools clamp down on religious expression, including speech that might oppose homosexuality or abortion.

The case is Morse v. Frederick, 06-278.