THE Constitution generally prohibits the government from suppressing words and images unless they are obscene. But the Supreme Court upheld a narrow exception to this free speech tenet in 1978, letting the Federal Communications Commission ban “indecent but not obscene” material from radio and television because it said broadcast media were pervasive and accessible to children.

In F.C.C. v. Fox Television Stations, which the court heard on Tuesday, the justices should overturn the 1978 ruling and apply the same First Amendment principles to all media. If the court refuses to go that far, it should at least uphold the decision by the United States Court of Appeals for the Second Circuit that the F.C.C.’s indecency policy is “unconstitutional because it is impermissibly vague” and must be revised to give reliable notice about what can be broadcast.

A revolution in communications has taken away the grounds for treating radio and television differently. As Justice Samuel Alito Jr.said in court on Tuesday, “Broadcast TV is living on borrowed time,” with cable and wireless communications being so widespread. Technology, like the V-chip in TVs and digital converter boxes, allows parents to block programs inappropriate for children.

The F.C.C.’s policy prohibits indecent material and profane speech between 6 a.m. and 10 p.m. Violations may result in substantial monetary fines, loss of a broadcast license and other sanctions.

The agency has applied this policy so inconsistently that, as a brief for ABC Inc. and others argued, “broadcasters have no way to know what material the commission will deem indecent.”