ON SEPTEMBER 18, 2001, ABC News president David Westin decided that his network would no longer air footage of the attacks on the World Trade Center only a week before. The constant repetition of the images of the planes crashing into the buildings had become "gratuitous," a spokesman said.

Almost immediately, all other networks and news channels adopted the same policy, and ever since, it is only on rare occasions that Americans have been exposed to those indelible images. This extraordinary act of journalistic collusion followed another mysteriously unanimous decision to censor the photographs and moving images of those victims who had chosen to jump to their deaths rather than be burned alive.

At the time, these choices seemed tasteful and appropriate. The perpetual repetition of the pictures and footage over the course of that first week threatened to make them as familiar as bland wallpaper, or serve as the permanent backdrop for cable-news channel self-promotion. And yet the policy has remained in place to this day, long after there was any risk of the footage's misuse.

Indeed, the purpose behind censoring the 9/11 images seems to be somewhat different from the one in the immediate aftermath of the attacks. One gets the impression that the video footage is kept largely under wraps because of the emotions it might provoke. Someone is trying to protect us from the neurochemical cocktail of grief and rage, sorrow and anger, trauma and vengefulness that even a few minutes' conversation about 9/11 can cause.

Or, perhaps, some in the media might feel as though the imagery is almost too politicized. Perhaps because George W. Bush invokes the attacks and their meaning so frequently, leading figures in the media believe the imagery will tend to buttress Bush's arguments, and serve as unpaid advertising for the president's policies.

Thus, while the events of 9/11 remain the most important and devastating in recent American history, they have achieved a peculiar invisibility. In New York, where I live, there are ferocious arguments about the way the rebuilding at Ground Zero has been mishandled--about the designs of the buildings and the street grid and the look, placement, and size of the memorials. Somehow, these discussions have become weirdly divorced from the reason that Ground Zero even exists.

And what of the country? In an April CBS News poll, only 6 percent of respondents said terrorism was the most important problem facing the United States. Even if that shockingly small number is misleading--because in the same poll, 27 percent of respondents said Iraq was the most important problem, and many of them surely believe the war in Iraq is part of the war on terror--it still indicates that the events of 9/11 have receded. Yes, everyone knows about and remembers the hijacking of four planes and the murders of nearly 3,000 civilians in an unprovoked and unprecedented attack. But those deaths may have lost some of their sting.

The masterful new film United 93, the first major Hollywood release about September 11, is reticent as well when it comes to the depictions of the attacks in New York. American Airlines Flight 11 is shown only as a computerized glyph on an air-traffic controller's screen. The controller knows the plane has been hijacked and is tracking it as it enters the airspace over New York. Suddenly, the glyph just vanishes from his screen.