Chief Justice John Roberts said in a written ruling that schools may prohibit student expression that can be interpreted as advocating the use of drugs.

Mr Frederick, 18 at the time, said the words on his 14ft (4.26m) banner did not relate to drug use and were meant to be funny in an attempt to get on television.

Head teacher Deborah Morse, who destroyed Mr Frederick's banner and suspended him for 10 days, argued that the banner's message went against the school's anti-drugs policy and was unfurled during a school event to watch the flame pass.

A bong is a type of water pipe that can be used to smoke marijuana.

Bush's backing

The Supreme Court's ruling has tightened limits on students' rights to free speech at school events.

Chief Justice Roberts wrote: "The message on Frederick's banner is cryptic. 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."

The court found that schools "may take steps to safeguard those entrusted to their care from speech that can reasonably be regarded as encouraging illegal drug use".

This meant Mr Frederick's constitutional free speech rights were not violated by the confiscation of his banner and his suspension, Chief Justice Roberts concluded.

Ms Morse and the Juneau school board were supported by the Bush administration, which wanted a broad rule that public schools do not have to tolerate speech that disrupts their basic educational mission.

Vietnam precedent

Mr Frederick, now 23 and studying and teaching in China, was backed in the case by the American Civil Liberties Union and the American Center for Law and Justice.

He was also supported by conservative groups concerned that a ruling against him could allow schools to limit students' expression of religious views, particularly on the issues of abortion and homosexuality.

Mr Frederick's lawyer, Douglas Mertz, argued that the court should stand by its 1969 ruling that students do not "shed their constitutional rights to freedom of speech or expression at the schoolhouse gate".

In that case, at the height of the Vietnam War, the Supreme Court decided in favour of students who wanted to wear black armbands in class to protest against the war.

But the court ruled in the late 1980s that a student did not have the right to give a sexually-suggestive speech at a school assembly and that school newspapers could be censored.